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 A350305 a(n) is the constant term in the expansion of Product_{k=1..n} (x^k + 1 + 1/x^k)^n. 3
 1, 1, 13, 1437, 1884211, 24657701475, 3111336932350947, 3710920324904591897521, 41323213770479673319301068309, 4261037235228828189774620497534270303, 4045313784246510024420372971256850718016451185 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS a(n) is the coefficient of x^(n^2 * (n+1)/2) in Product_{k=0..n} (1 + x^k + x^(2*k))^n. LINKS Robert Israel, Table of n, a(n) for n = 0..44 MAPLE f:= n -> coeff(mul(x^k+1+1/x^k, k=1..n)^n, x, 0): map(f, [\$0..12]); # Robert Israel, Jan 15 2023 MATHEMATICA a[n_] := Coefficient[Series[Product[(x^k + 1 + 1/x^k)^n, {k, 1, n}], {x, 0, 0}], x, 0]; Array[a, 11, 0] (* Amiram Eldar, Dec 24 2021 *) PROG (PARI) a(n) = polcoef(prod(k=1, n, x^k+1+1/x^k)^n, 0); (PARI) a(n) = polcoef(prod(k=1, n, 1+x^k+x^(2*k))^n, n^2*(n+1)/2); CROSSREFS Cf. A007576, A156181, A225602, A350282, A350306, A350307. Sequence in context: A238562 A196966 A203369 * A197097 A353030 A064962 Adjacent sequences: A350302 A350303 A350304 * A350306 A350307 A350308 KEYWORD nonn AUTHOR Seiichi Manyama, Dec 23 2021 STATUS approved

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Last modified June 1 03:55 EDT 2023. Contains 363068 sequences. (Running on oeis4.)