This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A075088 #18 Feb 14 2015 21:07:02 %S A075088 1,3,6,28,36,120,528,2080,2016,25200,32640,819840,131328,7874496, %T A075088 20476800,52433920,8386560,102767616,536887296,2147450880,26306560000, %U A075088 16240435200,116802736128,34359607296,2199022206976,549755289600 %N A075088 Smallest triangular number with n prime factors (counted with multiplicity). %H A075088 Donovan Johnson, <a href="/A075088/b075088.txt">Table of n, a(n) for n = 0..51</a> %e A075088 a(3)=28 because 28 is a triangular number with 3 prime factors: 28 = 2*2*7. %o A075088 (PARI) a(n)=if(n<0,0,s=1; while(abs(bigomega(s*(s+1)/2)-n)>0,s++); s*(s+1)/2) %Y A075088 Cf. A000217, A076550. %K A075088 nonn %O A075088 0,2 %A A075088 _Amarnath Murthy_, Sep 13 2002 %E A075088 More terms from _Benoit Cloitre_, Sep 17 2002 %E A075088 a(21)-a(24) from Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 15 2004 %E A075088 Edited by _Ray Chandler_, Dec 17 2004 %E A075088 a(25) from _Ray Chandler_, Dec 22 2004