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 A278404 #37 Nov 24 2016 12:06:11 %S A278404 3,9,29,101,346,247,6098,3181,2878,2531,16033,26615,114371,41793, %T A278404 74506,39359,463178,104677,248426,517441,923743,506531,1930846,584237, %U A278404 2560202,4036993,4570438,4552391,7879282,4417843,27841082,5167619,13683067,9725141,47735377,25045807,63305698 %N A278404 Greater number in the least prime-semiprime gap of size n. %C A278404 A prime-semiprime gap of n is defined as the difference between p & q, p being either a prime, A000040, or a semiprime, A001358, and q being the next greater prime or semiprime, see examples. %C A278404 The corresponding numbers at the start of the prime-semiprime gaps, i.e., a(n)-n, are in A278351. %H A278404 Bobby Jacobs, Charles R Greathouse IV, Jonathan Vos Post, and Robert G. Wilson v, <a href="/A278404/b278404.txt">Table of n, a(n) for n = 1..52</a> %e A278404 a(1) = 3 since there is a gap of 1 between 2 and 3, both of which are primes. %e A278404 a(2) = 9 since there is a gap of 2 between 7 and 9, the first is a prime and the second is a semiprime. %e A278404 a(3) = 29 since there is a gap of 3 between 26, a semiprime, and 29, a prime. %e A278404 a(6) = 247 because the first prime-semiprime gap of size 6 is between 241 and 247. %Y A278404 Cf. A037143, A275013, A275014, A275108, A278351. %K A278404 nonn %O A278404 1,1 %A A278404 _Bobby Jacobs_, _Charles R Greathouse IV_, _Jonathan Vos Post_, and _Robert G. Wilson v_, Nov 20 2016