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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
OFFSET
1,1
COMMENTS
The sum of divisors of 2m^2 [twice a square] always gives remainder r = 3 modulo 6. See A097022.
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
KEYWORD
nonn
AUTHOR
Labos Elemer, Nov 19 2001
STATUS
approved