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 A346041 #15 Jun 21 2024 17:08:32 %S A346041 4,6,8,9,10,14,15,16,21,22,25,26,27,32,33,34,35,38,39,46,49,51,55,57, %T A346041 58,62,64,65,69,74,77,81,82,85,86,87,91,93,94,95,106,111,115,118,119, %U A346041 121,122,123,125,128,129,133,134,141,142,143,145,146,155,158,159,161,166,169 %N A346041 Numbers with exactly 1 semiprime divisor. %C A346041 Numbers of the form p*q or p^k, where p and q are prime and k >= 2. %C A346041 Numbers k such that A086971(k) = 1. - _Wesley Ivan Hurt_, Jun 21 2024 %e A346041 6 is in the sequence since it has exactly 1 semiprime divisor, namely 6. %e A346041 16 is in the sequence since it has exactly 1 semiprime divisor, namely 4. %t A346041 Select[Range@200,Length@Select[Divisors@#,PrimeOmega@#==2&]==1&] (* _Giorgos Kalogeropoulos_, Jul 03 2021 *) %o A346041 (PARI) isok(k) = sumdiv(k, d, bigomega(d)==2) == 1; \\ _Michel Marcus_, Jul 03 2021 %o A346041 (Python) %o A346041 from sympy import factorint %o A346041 def ok(n): %o A346041 f = factorint(n); w = len(f); W = sum(f.values()) %o A346041 return (w == 1 and W >= 2) or (w == 2 and W == 2) %o A346041 print(list(filter(ok, range(170)))) # _Michael S. Branicky_, Jul 03 2021 %Y A346041 Cf. A001358 (semiprimes), A086971. %K A346041 nonn %O A346041 1,1 %A A346041 _Wesley Ivan Hurt_, Jul 02 2021