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 A158465 Number of solutions to +-1+-2^4+-3^4+-4^4...+-n^4=0. 0
 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 16, 18, 0, 0, 32, 100, 0, 0, 424, 510, 0, 0, 2792, 5988, 0, 0, 29058, 45106, 0, 0, 276828, 473854, 0, 0, 2455340, 4777436, 0, 0, 27466324, 46429640, 0, 0, 280395282, 526489336, 0, 0, 3193589950, 5661226928, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,16 COMMENTS Constant term in the expansion of (x + 1/x)(x^16 + 1/x^16)..(x^n^4 + 1/x^n^4). a(n)=0 for any n=1 (mod 4) or n=2 (mod 4). Andrica & Tomescu give a more general integral formula than the one below. The asymptotic formula below is a conjecture by Andrica & Ionascu; it remains unproven. - Jonathan Sondow, Nov 11 2013 LINKS D. Andrica and E. J. Ionascu, Variations on a result of Erdős and SurányiINTEGERS 2013 slides. Dorin Andrica and Ioan Tomescu, On an Integer Sequence Related to a Product of Trigonometric Functions, and Its Combinatorial Relevance, J. Integer Sequences, 5 (2002), Article 02.2.4. FORMULA Integral representation: a(n) = ((2^n)/Pi)*int_0^pi prod_{k=1}^n cos(x*k^4) dx. Asymptotic formula: a(n) = (2^n)*sqrt(18/(Pi*n^9))*(1+o(1)) as n->infinity; n=-1 or 0 (mod 4). EXAMPLE For n=16 the a(16) = 2 solutions are +1 +16 +81 +256 -625 -1296 -2401 +4096 +6561 +10000 +14641 +20736 -28561 -38416 -50625 +65536 = 0 and the opposite. MAPLE N:=32: p:=1 a:=[]: for n from 32 to N do p:=expand (p*(x^(n^4)+x^(-n^4))): a:=[op(a), coeff(p, x, 0)]: od:a; CROSSREFS Cf. A063865, A158092, A158118, A158380, A019568. A111253(n) = a(n)/2. - Alois P. Heinz, Oct 31 2011 Sequence in context: A191418 A120556 A120560 * A003193 A108474 A120582 Adjacent sequences:  A158462 A158463 A158464 * A158466 A158467 A158468 KEYWORD nonn AUTHOR Pietro Majer, Mar 19 2009 EXTENSIONS a(35)-a(58) from Alois P. Heinz, Oct 31 2011 STATUS approved

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Last modified January 19 06:28 EST 2021. Contains 340266 sequences. (Running on oeis4.)