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 A121478 #6 Oct 19 2024 15:46:32 %S A121478 66,78,105,120,190,231,276,300,378,406,435,465,528,561,595,666,741, %T A121478 820,861,903,946,1035,1128,1176,1275,1378,1485,1653,1953,2016,2080, %U A121478 2211,2278,2485,2556,2628,2775,3081,3160,3240,3655,3741,3916,4005,4371,4465 %N A121478 Triangular numbers with three distinct prime factors. %e A121478 11*12/2 = 2*3*11 = 66 is the smalles triangular number with three distinct prime factors, hence a(1) = 66. %t A121478 Select[Accumulate[Range[0, 100]] ,PrimeNu[#]==3&] (* _James C. McMahon_, Oct 19 2024 *) %o A121478 (PARI) for(n=1,100,k=binomial(n+1,2);if(omega(k)==3,print1(k,","))) %Y A121478 Cf. A000217, A068443, A119663, A121479. %K A121478 easy,nonn %O A121478 1,1 %A A121478 _Klaus Brockhaus_, Aug 01 2006