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 A305729 #61 Mar 17 2025 02:40:03 %S A305729 1,14,22,46,94,118,166,214,334,358,422,454,526,662,694,718,766,926, %T A305729 934,958,1006,1094,1126,1142,1174,1382,1438,1678,1718,1726,1774,1822, %U A305729 1934,1966,2038 %N A305729 Numbers k such that A000010(k) = A023900(k) and A000010(A023900(k)) = A023900(A000010(k)). %C A305729 For known terms with n > 1: %C A305729 - a(n) and phi(a(n)) are squarefree integers with an even number of prime factors. For example a(5) = 94 = 2 * 47, and phi(a(5)) = 46 = 2 * 23. %C A305729 - When omega(a(n)) = omega(phi(a(n))) = 2 then a(n)/2 are the safe primes (see A005385). %C A305729 - When omega(a(n)) = omega(phi(a(n))) = 2 then ((a(n)/2)-1)/2 = phi(a(n))/2 are the Sophie Germain primes (see A005384). %e A305729 1 is a term because A000010(1) = A023900(2) and A000010(A023900(1)) = A023900(A000010(1)). %Y A305729 Cf. A000010, A023900, A005384, A005385. %Y A305729 Cf. Subsequence of A244466. %Y A305729 Cf. Subsequence of A306146. %K A305729 nonn %O A305729 1,2 %A A305729 _Torlach Rush_, Aug 11 2018