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 A333771 #13 Jul 21 2021 17:20:34 %S A333771 210,1326,1770,1830,2145,2346,2415,2926,3003,3486,4186,4278,5565,6105, %T A333771 6555,6670,7626,8385,8646,9730,11935,12246,13695,16653,17205,17391, %U A333771 17578,18915,22155,22578,24531,25878,26106,27730,27966,28203,30381,32385,33411,35245 %N A333771 Triangular numbers that are the product of four distinct primes. %C A333771 The maximum exponent for each prime in the factorization of each term is one. - _Harvey P. Dale_, Jul 21 2021 %H A333771 Robert Israel, <a href="/A333771/b333771.txt">Table of n, a(n) for n = 1..10000</a> %e A333771 The 20th triangular number, T(20) = 20*21/2 = 210 = 2 * 3 * 5 * 7, so 210 is a term. %e A333771 T(1333) = 889111 = 23 * 29 * 31 * 43, so 889111 is a term. %p A333771 q:= n-> map(i-> i[2], ifactors(n)[2])=[1$4]: %p A333771 select(q, [seq(n*(n+1)/2, n=0..300)])[]; # _Alois P. Heinz_, Apr 04 2020 %t A333771 Select[Accumulate[Range[300]],PrimeNu[#]==PrimeOmega[#]==4&] (* _Harvey P. Dale_, Jul 21 2021 *) %Y A333771 Cf. A000217 (triangular numbers), A068443 (triangular numbers that are the product of 2 distinct primes), A128896 (triangular numbers that are the product of 3 distinct primes). %Y A333771 Cf. A076578, A121479. %K A333771 nonn %O A333771 1,1 %A A333771 _Jon E. Schoenfield_, Apr 04 2020