A064366 - OEIS

%I #24 Nov 04 2017 04:43:32

%S 1,3,6,21,15,66,28,1365,1716,3060,66,20475,91,134596,735471,7888725,

%T 153,3262623,190,118030185,225792840,254186856,276,2558620845,

%U 84672315,11058116888,113380261800,558383307300,435,11969016345,496

%N Special binomial coefficient: a(n) = C(sigma(n), phi(n)).

%H Harry J. Smith, <a href="/A064366/b064366.txt">Table of n, a(n) for n = 1..200</a>

%F a(n) = C(A000203(n), A000010(n)); at prime indices it gives triangular numbers (A034953(p)).

%t Array[Binomial[DivisorSigma[1, #], EulerPhi@ #] &, 31] (* _Michael De Vlieger_, Nov 03 2017 *)

%o (PARI) { for (n=1, 200, write("b064366.txt", n, " ", binomial(sigma(n), eulerphi(n))) ) } \\ _Harry J. Smith_, Sep 12 2009

%Y Cf. A000203, A000010, A034953, A066090, A066449.

%K nonn

%O 1,2

%A _Labos Elemer_, Sep 27 2001