A064366 a(n) = binomial(sigma(n), phi(n)).

1, 3, 6, 21, 15, 66, 28, 1365, 1716, 3060, 66, 20475, 91, 134596, 735471, 7888725, 153, 3262623, 190, 118030185, 225792840, 254186856, 276, 2558620845, 84672315, 11058116888, 113380261800, 558383307300, 435, 11969016345, 496, 366395202809685, 16735679449896, 21094923659355

Offset: 1

Author

Labos Elemer, Sep 27 2001

Keywords

• nonn

Links

• Harry J. Smith, Table of n, a(n) for n = 1..200

Crossrefs

Cf. A000010, A000203, A000217, A034953, A066090, A066449.

Programs

Mathematica

Array[Binomial[DivisorSigma[1, #], EulerPhi@ #] &, 31] (* Michael De Vlieger, Nov 03 2017 *)

PARI

a(n) = { binomial(sigma(n), eulerphi(n)) } \\ Harry J. Smith, Sep 12 2009

Formula

a(n) = binomial(A000203(n), A000010(n));

a(p) = A000217(p) for prime p.