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 A065765 Sum of divisors of twice square numbers. 6
 3, 15, 39, 63, 93, 195, 171, 255, 363, 465, 399, 819, 549, 855, 1209, 1023, 921, 1815, 1143, 1953, 2223, 1995, 1659, 3315, 2343, 2745, 3279, 3591, 2613, 6045, 2979, 4095, 5187, 4605, 5301, 7623, 4221, 5715, 7137, 7905, 5169, 11115, 5679, 8379, 11253 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The sum of divisors of 2m^2 [twice a square] always gives remainder r = 3 modulo 6. See A097022. LINKS T. D. Noe, Table of n, a(n) for n = 1..10000 FORMULA a(n) = sigma(2*n^2) = A000203(2*A000290(n)). a(n) = 3*A065766(n). Sum_{k=1..n} a(k) ~ c * n^3, where c = 12*zeta(3)/Pi^2 = 1.461525... . - Amiram Eldar, Oct 28 2022 MATHEMATICA DivisorSigma[1, 2*Range[50]^2] (* Harvey P. Dale, Sep 06 2015 *) PROG (PARI) { for (n=1, 10000, write("b065765.txt", n, " ", sigma(2*n^2)) ) } \\ Harry J. Smith, Oct 30 2009 CROSSREFS Cf. A000203, A000290, A002117, A028982, A065766, A097022. Sequence in context: A176661 A117561 A353679 * A318738 A146853 A183476 Adjacent sequences: A065762 A065763 A065764 * A065766 A065767 A065768 KEYWORD nonn AUTHOR Labos Elemer, Nov 19 2001 STATUS approved

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Last modified September 28 19:19 EDT 2023. Contains 365737 sequences. (Running on oeis4.)