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 A321831 a(n) = Sum_{d|n, n/d==1 mod 4} d^7 - Sum_{d|n, n/d==3 mod 4} d^7. 12
 1, 128, 2186, 16384, 78126, 279808, 823542, 2097152, 4780783, 10000128, 19487170, 35815424, 62748518, 105413376, 170783436, 268435456, 410338674, 611940224, 893871738, 1280016384, 1800262812, 2494357760, 3404825446, 4584374272, 6103593751 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Seiichi Manyama, Table of n, a(n) for n = 1..10000 J. W. L. Glaisher, On the representations of a number as the sum of two, four, six, eight, ten, and twelve squares, Quart. J. Math. 38 (1907), 1-62 (see p. 4 and p. 8). Index entries for sequences mentioned by Glaisher. FORMULA G.f.: Sum_{k>=1} k^7*x^k/(1 + x^(2*k)). - Ilya Gutkovskiy, Nov 26 2018 Multiplicative with a(p^e) = round(p^(7e+7)/(p^7 + p%4 - 2)), where p%4 is the remainder of p modulo 4. (Following R. Israel in A321833.) - M. F. Hasler, Nov 26 2018 Sum_{k=1..n} a(k) ~ c * n^8 / 8, where c = A258815. - Amiram Eldar, Nov 04 2023 MATHEMATICA s[n_, r_] := DivisorSum[n, #^7 &, Mod[n/#, 4]==r &]; a[n_] := s[n, 1] - s[n, 3]; Array[a, 30] (* Amiram Eldar, Nov 26 2018 *) s[n_] := If[OddQ[n], (-1)^((n-1)/2), 0]; (* A101455 *) f[p_, e_] := (p^(7*e+7) - s[p]^(e+1))/(p^7 - s[p]); a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* Amiram Eldar, Nov 04 2023 *) PROG (PARI) apply( A321831(n)=factorback(apply(f->f[1]^(7*f[2]+7)\/(f[1]^7+f[1]%4-2), Col(factor(n)))), [1..30]) \\ M. F. Hasler, Nov 26 2018 CROSSREFS Cf. A101455, A258815. Cf. A321543 - A321565, A321807 - A321836 for similar sequences. Glaisher's E'_i (i=0..12): A002654, A050469, A050470, A050471, A050468, A321829, A321830, this sequence, A321832, A321833, A321834, A321835, A321836. Sequence in context: A283338 A128696 A195594 * A351195 A223954 A224138 Adjacent sequences: A321828 A321829 A321830 * A321832 A321833 A321834 KEYWORD nonn,easy,mult AUTHOR N. J. A. Sloane, Nov 24 2018 STATUS approved

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Last modified November 30 03:08 EST 2023. Contains 367452 sequences. (Running on oeis4.)