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A294099
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Rectangular array read by (upward) antidiagonals: A(n,k) = Sum_{j=0..k} (-1)^floor(j/2)*binomial(k-floor((j+1)/2), floor(j/2))*n^(k-j), n >= 1, k >= 0.
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17
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1, 1, 2, 1, 3, 1, 1, 4, 5, -1, 1, 5, 11, 7, -2, 1, 6, 19, 29, 9, -1, 1, 7, 29, 71, 76, 11, 1, 1, 8, 41, 139, 265, 199, 13, 2, 1, 9, 55, 239, 666, 989, 521, 15, 1, 1, 10, 71, 377, 1393, 3191, 3691, 1364, 17, -1, 1, 11, 89, 559, 2584, 8119, 15289, 13775, 3571, 19, -2
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OFFSET
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1,3
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COMMENTS
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This array is used to compute A269254: A269254(n) = least k such that A(n,k) is a prime, or -1 if no such k exists.
The array can be extended to k<0 with A(n, k) = -A(n, -k-1) for all k in Z. - Michael Somos, Jun 19 2023
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LINKS
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FORMULA
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A(n,0) = 1, A(n,1) = n + 1, A(n,k) = n*A(n,k-1) - A(n,k-2), n >= 1, k >= 2.
G.f. for row n: (1 + x)/(1 - n*x + x^2), n >= 1.
A(n, k) = B(-n, k) where B = A29045. - Michael Somos, Jun 19 2023
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EXAMPLE
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Array begins:
1 2 1 -1 -2 -1 1 2 1 -1
1 3 5 7 9 11 13 15 17 19
1 4 11 29 76 199 521 1364 3571 9349
1 5 19 71 265 989 3691 13775 51409 191861
1 6 29 139 666 3191 15289 73254 350981 1681651
1 7 41 239 1393 8119 47321 275807 1607521 9369319
1 8 55 377 2584 17711 121393 832040 5702887 39088169
1 9 71 559 4401 34649 272791 2147679 16908641 133121449
1 10 89 791 7030 62479 555281 4935050 43860169 389806471
1 11 109 1079 10681 105731 1046629 10360559 102558961 1015229051
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MATHEMATICA
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(* Array: *)
Grid[Table[LinearRecurrence[{n, -1}, {1, 1 + n}, 10], {n, 10}]]
(* Array antidiagonals flattened (gives this sequence): *)
A294099[n_, k_] := Sum[(-1)^(Floor[j/2]) Binomial[k - Floor[(j + 1)/2], Floor[j/2]] n^(k - j), {j, 0, k}]; Flatten[Table[A294099[n - k, k], {n, 11}, {k, 0, n - 1}]]
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PROG
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(PARI) {A(n, k) = sum(j=0, k, (-1)^(j\2)*binomial(k-(j+1)\2, j\2)*n^(k-j))}; /* Michael Somos, Jun 19 2023 */
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CROSSREFS
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Cf. A285992, A299107, A299109, A088165, A117522, A299100, A299101, A113501, A269253, A269254, A294099, A298675, A298677, A298878, A299045, A299071.
Rows: A057079, A005408, A002878, A001834, A030221, A002315, A033890, A057080, A057081, A054320, ...
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KEYWORD
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AUTHOR
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STATUS
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approved
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