|
%I #14 Oct 02 2013 15:47:19
%S 1,3,6,66,210,3570,103740,930930,56812470,1722580860,32395433070,
%T 265257422430,91348974206490,8923863379851420,330196858581850260,
%U 14193386885746698630,2378522762792139793830,351206814022419685159830,28791787439593010836313310
%N Smallest triangular number with n prime factors (counted without multiplicity).
%C a(19) <= 8285055066500101241048306610. a(20) <= 120052594044654305809137933570. - _Donovan Johnson_, Feb 28 2012
%e a(0) = 1 because 1 is a triangular number with zero prime factors; a(3) = 66 because 66 = 2*3*11 is a triangular number with 3 distinct prime factors.
%o (PARI) {n=12; v=vector(n); for(k=1,1000000,t=k*(k+1)/2; d=1+omega(t); if(d<=n&&v[d]<1,v[d]=t)); for(j=1,n,print1(v[j],","))}
%Y Cf. A000217, A127637.
%K nonn
%O 0,2
%A _Shyam Sunder Gupta_, Oct 19 2002
%E a(12) from _Rick L. Shepherd_, May 31 2003
%E a(13) from _Klaus Brockhaus_, Aug 02 2006
%E a(14)-a(16) from _Donovan Johnson_, Jan 28 2009
%E a(17) from _Donovan Johnson_, Feb 07 2009
%E a(18) from _Donovan Johnson_, Feb 28 2012
|
