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Mirrors > Home > ILE Home > Th. List > mulsucdiv2z | GIF version |
Description: An integer multiplied with its successor divided by 2 yields an integer, i.e. an integer multiplied with its successor is even. (Contributed by AV, 19-Jul-2021.) |
Ref | Expression |
---|---|
mulsucdiv2z | ⊢ (𝑁 ∈ ℤ → ((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | zeo 8452 | . 2 ⊢ (𝑁 ∈ ℤ → ((𝑁 / 2) ∈ ℤ ∨ ((𝑁 + 1) / 2) ∈ ℤ)) | |
2 | peano2z 8387 | . . . . . 6 ⊢ (𝑁 ∈ ℤ → (𝑁 + 1) ∈ ℤ) | |
3 | zmulcl 8404 | . . . . . 6 ⊢ (((𝑁 / 2) ∈ ℤ ∧ (𝑁 + 1) ∈ ℤ) → ((𝑁 / 2) · (𝑁 + 1)) ∈ ℤ) | |
4 | 2, 3 | sylan2 280 | . . . . 5 ⊢ (((𝑁 / 2) ∈ ℤ ∧ 𝑁 ∈ ℤ) → ((𝑁 / 2) · (𝑁 + 1)) ∈ ℤ) |
5 | zcn 8356 | . . . . . . . 8 ⊢ (𝑁 ∈ ℤ → 𝑁 ∈ ℂ) | |
6 | 2 | zcnd 8470 | . . . . . . . 8 ⊢ (𝑁 ∈ ℤ → (𝑁 + 1) ∈ ℂ) |
7 | 2cnd 8112 | . . . . . . . 8 ⊢ (𝑁 ∈ ℤ → 2 ∈ ℂ) | |
8 | 2ap0 8132 | . . . . . . . . 9 ⊢ 2 # 0 | |
9 | 8 | a1i 9 | . . . . . . . 8 ⊢ (𝑁 ∈ ℤ → 2 # 0) |
10 | 5, 6, 7, 9 | div23apd 7914 | . . . . . . 7 ⊢ (𝑁 ∈ ℤ → ((𝑁 · (𝑁 + 1)) / 2) = ((𝑁 / 2) · (𝑁 + 1))) |
11 | 10 | eleq1d 2147 | . . . . . 6 ⊢ (𝑁 ∈ ℤ → (((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ ↔ ((𝑁 / 2) · (𝑁 + 1)) ∈ ℤ)) |
12 | 11 | adantl 271 | . . . . 5 ⊢ (((𝑁 / 2) ∈ ℤ ∧ 𝑁 ∈ ℤ) → (((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ ↔ ((𝑁 / 2) · (𝑁 + 1)) ∈ ℤ)) |
13 | 4, 12 | mpbird 165 | . . . 4 ⊢ (((𝑁 / 2) ∈ ℤ ∧ 𝑁 ∈ ℤ) → ((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ) |
14 | 13 | ex 113 | . . 3 ⊢ ((𝑁 / 2) ∈ ℤ → (𝑁 ∈ ℤ → ((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ)) |
15 | zmulcl 8404 | . . . . . 6 ⊢ ((𝑁 ∈ ℤ ∧ ((𝑁 + 1) / 2) ∈ ℤ) → (𝑁 · ((𝑁 + 1) / 2)) ∈ ℤ) | |
16 | 15 | ancoms 264 | . . . . 5 ⊢ ((((𝑁 + 1) / 2) ∈ ℤ ∧ 𝑁 ∈ ℤ) → (𝑁 · ((𝑁 + 1) / 2)) ∈ ℤ) |
17 | 5, 6, 7, 9 | divassapd 7912 | . . . . . . 7 ⊢ (𝑁 ∈ ℤ → ((𝑁 · (𝑁 + 1)) / 2) = (𝑁 · ((𝑁 + 1) / 2))) |
18 | 17 | eleq1d 2147 | . . . . . 6 ⊢ (𝑁 ∈ ℤ → (((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ ↔ (𝑁 · ((𝑁 + 1) / 2)) ∈ ℤ)) |
19 | 18 | adantl 271 | . . . . 5 ⊢ ((((𝑁 + 1) / 2) ∈ ℤ ∧ 𝑁 ∈ ℤ) → (((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ ↔ (𝑁 · ((𝑁 + 1) / 2)) ∈ ℤ)) |
20 | 16, 19 | mpbird 165 | . . . 4 ⊢ ((((𝑁 + 1) / 2) ∈ ℤ ∧ 𝑁 ∈ ℤ) → ((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ) |
21 | 20 | ex 113 | . . 3 ⊢ (((𝑁 + 1) / 2) ∈ ℤ → (𝑁 ∈ ℤ → ((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ)) |
22 | 14, 21 | jaoi 668 | . 2 ⊢ (((𝑁 / 2) ∈ ℤ ∨ ((𝑁 + 1) / 2) ∈ ℤ) → (𝑁 ∈ ℤ → ((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ)) |
23 | 1, 22 | mpcom 36 | 1 ⊢ (𝑁 ∈ ℤ → ((𝑁 · (𝑁 + 1)) / 2) ∈ ℤ) |
Colors of variables: wff set class |
Syntax hints: → wi 4 ∧ wa 102 ↔ wb 103 ∨ wo 661 ∈ wcel 1433 class class class wbr 3785 (class class class)co 5532 0cc0 6981 1c1 6982 + caddc 6984 · cmul 6986 # cap 7681 / cdiv 7760 2c2 8089 ℤcz 8351 |
This theorem was proved from axioms: ax-1 5 ax-2 6 ax-mp 7 ax-ia1 104 ax-ia2 105 ax-ia3 106 ax-in1 576 ax-in2 577 ax-io 662 ax-5 1376 ax-7 1377 ax-gen 1378 ax-ie1 1422 ax-ie2 1423 ax-8 1435 ax-10 1436 ax-11 1437 ax-i12 1438 ax-bndl 1439 ax-4 1440 ax-13 1444 ax-14 1445 ax-17 1459 ax-i9 1463 ax-ial 1467 ax-i5r 1468 ax-ext 2063 ax-sep 3896 ax-pow 3948 ax-pr 3964 ax-un 4188 ax-setind 4280 ax-cnex 7067 ax-resscn 7068 ax-1cn 7069 ax-1re 7070 ax-icn 7071 ax-addcl 7072 ax-addrcl 7073 ax-mulcl 7074 ax-mulrcl 7075 ax-addcom 7076 ax-mulcom 7077 ax-addass 7078 ax-mulass 7079 ax-distr 7080 ax-i2m1 7081 ax-0lt1 7082 ax-1rid 7083 ax-0id 7084 ax-rnegex 7085 ax-precex 7086 ax-cnre 7087 ax-pre-ltirr 7088 ax-pre-ltwlin 7089 ax-pre-lttrn 7090 ax-pre-apti 7091 ax-pre-ltadd 7092 ax-pre-mulgt0 7093 ax-pre-mulext 7094 |
This theorem depends on definitions: df-bi 115 df-3or 920 df-3an 921 df-tru 1287 df-fal 1290 df-nf 1390 df-sb 1686 df-eu 1944 df-mo 1945 df-clab 2068 df-cleq 2074 df-clel 2077 df-nfc 2208 df-ne 2246 df-nel 2340 df-ral 2353 df-rex 2354 df-reu 2355 df-rmo 2356 df-rab 2357 df-v 2603 df-sbc 2816 df-dif 2975 df-un 2977 df-in 2979 df-ss 2986 df-pw 3384 df-sn 3404 df-pr 3405 df-op 3407 df-uni 3602 df-int 3637 df-br 3786 df-opab 3840 df-id 4048 df-po 4051 df-iso 4052 df-xp 4369 df-rel 4370 df-cnv 4371 df-co 4372 df-dm 4373 df-iota 4887 df-fun 4924 df-fv 4930 df-riota 5488 df-ov 5535 df-oprab 5536 df-mpt2 5537 df-pnf 7155 df-mnf 7156 df-xr 7157 df-ltxr 7158 df-le 7159 df-sub 7281 df-neg 7282 df-reap 7675 df-ap 7682 df-div 7761 df-inn 8040 df-2 8098 df-n0 8289 df-z 8352 |
This theorem is referenced by: sqoddm1div8z 10286 |
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