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 A023589 #9 Jul 09 2022 15:36:07 %S A023589 1,1,1,2,1,1,2,2,1,1,2,2,1,2,2,1,2,2,2,2,2,2,1,1,3,2,2,2,2,1,3,1,2,2, %T A023589 2,2,3,2,2,1,1,2,1,2,2,3,2,2,3,2,1,1,3,1,2,2,2,2,3,1,2,1,3,2,3,2,3,2, %U A023589 2,2,2,1,3,2,3,2,2,3,2,3,1,2,1,2,2,1,2,3,2,2,3,2,3,1,2,2,1,2,2 %N A023589 a(n) is the number of distinct prime divisors of 2*prime(n)+1. %H A023589 Michael De Vlieger, <a href="/A023589/b023589.txt">Table of n, a(n) for n = 1..10000</a> %t A023589 Array[PrimeNu[2 Prime[#] + 1] &, 99] (* _Michael De Vlieger_, Jul 09 2022 *) %o A023589 (PARI) a(n) = omega(2*prime(n)+1) \\ _Hugo Pfoertner_, Jul 09 2022 %Y A023589 Cf. A001221, A072055. %K A023589 nonn %O A023589 1,4 %A A023589 _Clark Kimberling_