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 A162308 #6 Feb 24 2019 20:04:30 %S A162308 0,7,9,11,11,13,15,15,15,15,19,19,19,23,23,23,23,29,29,31,33,33,33,35, %T A162308 37,37,39,39,39,41,41,41,41,41,41,41,41,41,41,45,45,45,45,47,47,47,47, %U A162308 47,47,47,49,49,49,49,51,51,51,53,53,55,57,57,59,59,59,59,59,59,59 %N A162308 Number of twin primes A001097 smaller than the non-twin prime A007510(n). %e A162308 a(2)=7 counts the numbers 3, 5, 7, 11, 13, 17, 19 below 23=A007510(2). %p A162308 isA007510 := proc(n) RETURN(isprime(n) and not isprime(n-2) and not isprime(n+2)) ; end: %p A162308 isA001097 := proc(n) RETURN(isprime(n) and (isprime(n-2) or isprime(n+2)) ) ; end: %p A162308 A007510 := proc(n) local a; if n = 1 then 2; else for a from procname(n-1)+1 do if isA007510(a) then RETURN(a) ; fi; od: fi; end: %p A162308 A162308 := proc(n) local a,k; a := 0 ; for k from 3 to A007510(n)-1 do if isA001097(k) then a := a+1; fi; od; a; end: %p A162308 seq(A162308(n),n=1..120) ; # _R. J. Mathar_, Jul 02 2009 %Y A162308 Cf. A000040, A073425. %K A162308 nonn %O A162308 1,2 %A A162308 _Juri-Stepan Gerasimov_, Jul 01 2009 %E A162308 Edited by _R. J. Mathar_, Jul 02 2009