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 A127913 #8 Sep 07 2025 08:58:37
%S A127913 3,0,2,1,6,1,7,2,2,9,10,1,6,1,9,6,2,9,6,2,1,11,6,9,2,3,1,22,5,18,2,9,
%T A127913 10,1,18,5,10,1,14,13,6,18,5,18,1,10,15,13,10,1,18,25,26,2,9,6,1,14,6,
%U A127913 7,9,9,2,1,18,1,18,2,9,2,21,9,6,5,22,11,1,2,1,18,5,10,1,2,13,42,1,18,5,1,2
%N A127913 Least k >= 0 such that A001597(n)+k is an even semiprime.
%e A127913 A001597(5) = 16. Among 16+0 = 16, 16+1 = 17, 16+2 = 18 = 2*3*3, 16+3 = 19, 16+4 = 20 = 2*2*5, 16+5 = 21 = 3*7 there is no even semiprime, but 16+6 = 22 = 2*11 is an even semiprime. Hence a(5) = 6.
%e A127913 A001597(14) = 121. 121+0 = 121 = 11*11 is not even, but 121+1 = 122 = 2*61 is an even semiprime. Hence a(14) = 1.
%o A127913 (Magma) PP:=[1] cat [ n: n in [2..5184] | IsPower(n) ]; [ k: p in PP | exists(k) {x: x in [0..100000] | IsEven(p+x) and IsPrime((p+x) div 2) } ]; /* _Klaus Brockhaus_, Apr 09 2007 */
%Y A127913 Cf. A001597 (perfect powers).
%K A127913 easy,nonn,changed
%O A127913 1,1
%A A127913 _Giovanni Teofilatto_, Apr 06 2007
%E A127913 Edited, corrected and extended by _Klaus Brockhaus_, Apr 09 2007