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 A275940 #13 Jan 25 2025 03:14:38 %S A275940 2,3,3,5,3,7,3,7,3,5,3,13,3,3,3,7,3,3,5,3,17,5,3,3,19,5,3,3,13,3,3,3, %T A275940 3,3,5,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,5,3,3,3,7,3,3,3,3,3,3,3,3,3,3, %U A275940 3,11,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,7 %N A275940 a(n) = A000005(A023194(n)). %C A275940 All the terms are primes. - _Amiram Eldar_, Jan 25 2025 %H A275940 Amiram Eldar, <a href="/A275940/b275940.txt">Table of n, a(n) for n = 1..10000</a> %e A275940 a(5) = A000005(A023194(5)) = A000005(25) = 3. %t A275940 DivisorSigma[0, #] &@ Prepend[Select[Range[5000]^2, PrimeQ[DivisorSigma[1, #]] &], 2] (* _Michael De Vlieger_, Aug 14 2016, after _Harvey P. Dale_ at A023194 *) %o A275940 (PARI) lista(nn) = for(n=1, nn, if(isprime(sigma(n)), print1(numdiv(n), ", "))); %Y A275940 Cf. A000005, A023194. %K A275940 nonn %O A275940 1,1 %A A275940 _Altug Alkan_, Aug 13 2016