A378200 Square array read by upward antidiagonals: T(n,k) = ((k + n - 1)^2 + (k - n + 1)*(-1)^n + (1 - k - n)*(-1)^k + (1 - k - n)*(-1)^(k + n) + 2)/2.
1, 5, 2, 6, 3, 4, 12, 9, 14, 7, 15, 8, 13, 10, 11, 23, 20, 25, 18, 27, 16, 28, 17, 26, 19, 24, 21, 22, 38, 35, 40, 33, 42, 31, 44, 29, 45, 30, 43, 32, 41, 34, 39, 36, 37, 57, 54, 59, 52, 61, 50, 63, 48, 65, 46, 66, 47, 64, 49, 62, 51, 60, 53, 58, 55, 56
Offset: 1
Examples
Table begins: 1, 2, 4, 7, 11, ... 5, 3, 14, 10, 27, ... 6, 9, 13, 18, 24, ... 12, 8, 25, 19, 42, ... 15, 20, 26, 33, 41, ... ... The first 5 antidiagonals are: 1; 5, 2; 6, 3, 4; 12, 9, 14, 7; 15, 8, 13, 10, 11; Triangle array begins: k= 1 2 3 4 5 6 7 8 9 n=1: 1; n=2: 5, 2, 6, 3, 4; n=3: 12, 9, 14, 7, 15, 8, 13, 10, 11; Subtracting (n-1)*(2*n-3) from each term is row n produces a permutation of numbers from 1 to 4*n-3: 1; 4, 1, 5, 2, 3; 6, 3, 8, 1, 9, 2, 7, 4, 5.
Links
- Boris Putievskiy, Table of n, a(n) for n = 1..9870
- Boris Putievskiy, Integer Sequences: Irregular Arrays and Intra-Block Permutations, arXiv:2310.18466 [math.CO], 2023.
- Boris Putievskiy, The Alternating Group A4: Subgroups and the Cayley Table (2025).
- Eric Weisstein's World of Mathematics, Alternating Group.
- Index entries for sequences that are permutations of the natural numbers.
Crossrefs
Programs
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Mathematica
T[n_, k_] := ((k + n - 1)^2 + (k - n + 1)*(-1)^n + (1 - k - n)*(-1)^k + (1 - k - n)*(-1)^(k + n) + 2)/2; Table[T[k, n], {k, 1, 5}, {n, 1, 5}]
Formula
Triangular array T(n,k) for 1 <= k <= 4n - 3 (see Example): T(n,k) = A000384(n-1) + P(n,k), P(n,k) = m + k if k < m and k == 1 (mod 2), P(n,k) = m - k if k < m and k == 0 (mod 2), P(n,k) = 3m - k - 1 if k >= m and k == 1 (mod 2), P(n,k)= - m + k + 1 if k >= m and k == 0 (mod 2), where m = 2n - 1.
G.f.: x*y*(1 + y + y^3 + y^4 - x^3*(2 + y + y^2 - 5*y^3 + y^4) + x*(4 - 3*y + y^2 - y^3 - y^4) - x^2*(1 - 3*y + 9*y^2 + 3*y^3 - 2*y^4) + x^4*(2 + y^2 - 2*y^3 + 3*y^4))/((1 - x)^3*(1 + x)^2*(1 - y)^3*(1 + y)^2). - Stefano Spezia, Jan 12 2025
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