A281590 - OEIS

A281590

Indices k such that A284896(k-1) and A284896(k) have a different sign.

1, 4, 9, 15, 20, 27, 33, 41, 48, 56, 64, 72, 80, 89, 98, 107, 116, 126, 136, 146, 156, 166, 176, 187, 198, 208, 219, 231, 242, 253, 265, 276, 288, 300, 312, 324, 337, 349, 362, 374, 387, 400, 413, 426, 439, 452, 465, 479, 492, 506, 519, 533, 547, 561, 575

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OFFSET

1,2

LINKS

Vaclav Kotesovec, Table of n, a(n) for n = 1..2612

EXAMPLE

A284896(8) = 73, A284896(9) = -45, sign is changed, so 9 is in the sequence.

A284896(14) = -66, A284896(15) = 2794, sign is changed, so 15 is in the sequence.

MATHEMATICA

nmax = 1000; A284896 = Rest[CoefficientList[Series[Product[1/(1 + x^k)^(k^2), {k, 1, nmax}], {x, 0, nmax}], x]]; csign = {1}; Do[If[(A284896[[n]] < 0 && A284896[[n+1]] >= 0) || (A284896[[n]] >= 0 && A284896[[n+1]] < 0), csign = Flatten[{csign, n + 1}]], {n, 1, Length[A284896] - 1}]; csign

CROSSREFS

Cf. A284896, A281591.

Sequence in context: A189459 A313272 A301680 * A112781 A166131 A313273

Adjacent sequences: A281587 A281588 A281589 * A281591 A281592 A281593

KEYWORD

nonn

AUTHOR

Vaclav Kotesovec, Apr 14 2017

STATUS

approved