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 A177997 #16 Mar 20 2018 19:02:32 %S A177997 2,5,7,13,31,41,43,59,101,107,127,137,149,199,239,277,359,389,479,613, %T A177997 743,757,809,829,937,991,1031,1103,1439,1487,1499,1847,1877,2011,2083, %U A177997 2179,2609,2663,2711,2741,2749,2857,2909,3329,3559,3623,3643,3697,3823 %N A177997 p and A002808(p)/2 are both prime. %C A177997 Primes p such that composite(p) is an even semiprime. %H A177997 Robert Israel, <a href="/A177997/b177997.txt">Table of n, a(n) for n = 1..10000</a> %e A177997 a(1)=2 because 2=prime and composite(2)/2=6/2=3=prime. %p A177997 P,C:= selectremove(isprime, [$2..10000]): %p A177997 select(t -> t <= nops(C) and C[t]::even and isprime(C[t]/2), P); # _Robert Israel_, Mar 20 2018 %o A177997 (PARI) %o A177997 c=[]; for(n=2, 10000, if(!isprime(n), c=concat(c, n))); c; \\ The composites %o A177997 s=[]; forprime(p=2, #c, if(c[p]%2==0 && isprime(c[p]\2), s=concat(s, p))); s \\ _Colin Barker_, Jun 28 2014 %Y A177997 Cf. A002808, A065858, A065897. %K A177997 nonn %O A177997 1,1 %A A177997 _Juri-Stepan Gerasimov_, May 17 2010, May 23 2010 %E A177997 Corrected by _D. S. McNeil_ and _R. J. Mathar_, May 23 2010