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 A216684 #19 Nov 15 2015 22:59:04 %S A216684 2,5,13,31,37,61,127,379,439,571,619,739,829,991,1549,3109,3301,3319, %T A216684 5749,7549,7879,48799 %N A216684 Primes p such that p - phi(k)^2 is not prime for 1 <= phi(k)^2 < p. %C A216684 phi is the Euler totient function phi(n) : A000010. %C A216684 A065377 is included in this sequence, and that one is probably finite. %C A216684 No more terms < 10^7. - _Robert Israel_, Nov 15 2015 %e A216684 31 is in the sequence because : %e A216684 31 - phi(1)^2 = 31 - 1^2 = 30 is composite; %e A216684 31 - phi(2)^2 = 31 - 1^2 = 30 is composite; %e A216684 31 - phi(3)^2 = 31 - 2^2 = 27 is composite; %e A216684 31 - phi(4)^2 = 31 - 2^2 = 27 is composite; %e A216684 31 - phi(5)^2 = 31 - 4^2 = 15 is composite; %e A216684 31 - phi(6)^2 = 31 - 2^2 = 27 is the last composite because phi(7)^2 = 6^2 > 31. %p A216684 with(numtheory):for n from 1 to 10000 do:ii:=0:p:=ithprime(n):for k from 1 to p while(p-phi(k)^2>0) do: if type(p- phi(k)^2,prime) =true then ii:=1:else fi:od:if ii=0 then printf(`%d, `,p):else fi:od: %Y A216684 Cf. A000010, A065377. %K A216684 nonn,more %O A216684 1,1 %A A216684 _Michel Lagneau_, Sep 15 2012