The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

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