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 A375385 #13 Aug 18 2024 11:44:23 %S A375385 15,1891,3403,5671,12403,15931,64261,73153,104653,114481,188191, %T A375385 226801,286903,351541,371953,392941,497503,518671,597871,665281, %U A375385 703891,853471,933661,1034641,1104841,1159003,1309771,1537381,1660753,1755001,1987021,2077741,3022111,3270403,3913003,4142881,4567753 %N A375385 Triangular numbers that are emirpimes. %C A375385 A number is an emirpimes if it is a semiprime and if its reverse is a different semiprime. Thus palindromic semiprimes are excluded. %e A375385 15 is the 5th triangular number. 15 = 3 * 5 and 51 = 3 * 17 are both semiprimes. %e A375385 1891 is the 61st triangular number. 1891 = 31 * 61 and 1981 = 7 * 283 are both semiprimes. %e A375385 3403 is the 82nd triangular number. 3403 = 41 * 83 and 3043 = 17 * 179 are both semiprimes. %t A375385 Select[Accumulate[Range[3200]], ! PalindromeQ[#] && PrimeOmega[#] == 2 && PrimeOmega[IntegerReverse[#]] == 2 &] (* _Amiram Eldar_, Aug 13 2024 *) %Y A375385 Intersection of A000217 and A097393. %K A375385 nonn,base %O A375385 1,1 %A A375385 _Massimo Kofler_, Aug 13 2024