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 A256388 #12 Apr 26 2016 09:03:16 %S A256388 1,3,9,15,27,39,57,69,99,105,135,147,177,189,195,225,237,267,279,309, %T A256388 345,417,429,459,519,567,597,615,639,657,807,819,825,855,879,1017, %U A256388 1029,1047,1059,1089,1149,1227,1275,1287,1299,1317,1425,1449,1479,1485,1605 %N A256388 Numbers n such that a single prime is the arithmetic mean of 2 semiprimes whose difference is 2*n. %C A256388 That is, there is a single prime p, such that p+n and p-n are both semiprime. %C A256388 Subsequence of A256389. %F A256388 Conjecture: a(n) = A001359(n)-2. - _Benedict W. J. Irwin_, Apr 26 2016 %e A256388 A256381 is the list of numbers n such that n-3 and n+3 are semiprimes, and it contains a single prime, hence 3 is in the sequence. %Y A256388 Cf. A124936, A256381. %Y A256388 Cf. A256387 (no prime), A256389 (one or more primes). %K A256388 nonn %O A256388 1,2 %A A256388 _Michel Marcus_, Mar 27 2015