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 A351867 #22 Mar 10 2025 14:48:45 %S A351867 3010,4774,10465,14326,20566,28462,54538,59059,59830,66178,66994, %T A351867 87142,104755,112042,120670,121771,131905,137710,138886,168610,179158, %U A351867 201214,212722,223054,249166,273406,288490,290191,314530,343546,358534,375778,401401,405418,419635,461605 %N A351867 Heptagonal numbers which are products of four distinct primes. %C A351867 A squarefree subsequence of heptagonal numbers. %e A351867 3010 = 2*5*7*43 = 35(5*35-3)/2. %e A351867 4774 = 2*7*11*31 = 44(5*44-3)/2. %e A351867 10465 = 5*7*13*23 = 65(5*65-3)/2. %e A351867 14326 = 2*13*19*29 = 76(5*76-3)/2. %o A351867 (Python) %o A351867 from itertools import count, islice %o A351867 from sympy import factorint %o A351867 def A351867_gen(): return filter(lambda k:sum((f := factorint(k)).values()) == 4 == len(f), (n*(5*n-3)//2 for n in count(1))) %o A351867 A351867_list = list(islice(A351867_gen(),20)) # _Chai Wah Wu_, Apr 14 2022 %Y A351867 Intersection of A000566 and A046386. %K A351867 nonn %O A351867 1,1 %A A351867 _Massimo Kofler_, Apr 12 2022