A068905 - OEIS

%I #13 Apr 23 2017 01:00:30

%S 1,3,4,7,6,66,8,15,13,153,12,378,14,276,276,31,18,741,20,861,496,630,

%T 24,1770,31,861,40,1540,30,59640,32,63,1128,1431,1128,4095,38,1770,

%U 1540,4005,42,142880,44,3486,3003,2556,48,7626

%N Binomial(sigma(n),omega(n)), where sigma(n) is the sum of divisors of n (A000203) and omega the number of distinct prime factors (A001221).

%H G. C. Greubel, <a href="/A068905/b068905.txt">Table of n, a(n) for n = 1..1000</a>

%t Binomial[DivisorSigma[1,#],Length[FactorInteger[#]]]&/@Range[50]  (* _Harvey P. Dale_, Feb 18 2011 *)

%o (PARI) a(n)=binomial(sigma(n),omega(n)) \\ _Charles R Greathouse IV_, Feb 19 2013

%Y Cf. A068903, A068904.

%K nonn

%O 1,2

%A _Reinhard Zumkeller_, Mar 06 2002