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A108223 a(n) = sigma_{2n}(n^2)/sigma_n(n^2), where sigma_n(m) = Sum_{k|m} k^n. 0
1, 13, 703, 61681, 9762501, 2140365529, 678222249307, 280379743338241, 150087010086914941, 99902428887422922553, 81402749386554449442711, 79477293980103609858493681, 91733330193268313783293023757, 123469159731637675342948027295569, 191751045863140709562160603031808243 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..15.

FORMULA

a(n) = Product_{p=primes} (Sum_{k=0..2*b(n, p)} p^(n*k)*(-1)^k), where p^b(n, p) is the highest power of p dividing n.

EXAMPLE

sigma_4(4)/sigma_2(4) =

(1 + 2^4 + 4^4)/(1 + 2^2 + 4^2) = 13.

MATHEMATICA

Table[DivisorSigma[2n, n^2]/DivisorSigma[n, n^2], {n, 10}] (* Ryan Propper, Apr 03 2007 *)

PROG

(PARI) a(n) = sigma(n^2, 2*n)/sigma(n^2, n); \\ Michel Marcus, Sep 06 2019

CROSSREFS

Cf. A062755.

Sequence in context: A113093 A195576 A195555 * A114355 A297748 A086157

Adjacent sequences:  A108220 A108221 A108222 * A108224 A108225 A108226

KEYWORD

nonn

AUTHOR

Leroy Quet, Jun 28 2005

EXTENSIONS

More terms from Ryan Propper, Apr 03 2007

More terms from Michel Marcus, Sep 06 2019

STATUS

approved

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Last modified January 28 23:12 EST 2022. Contains 350670 sequences. (Running on oeis4.)