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 A063681 #8 May 10 2014 17:12:56 %S A063681 37,265717,193710241,1270932914161, %T A063681 187855106306818130162790081799568953899918191769361, %U A063681 884821727139988111281341588371104523273965529248966451172919369920848760385637 %N A063681 Primes p such that 2p+7 is a power of three. %C A063681 If (3^i-7)/2 is prime then x=3^i-7 is a solution of sigma(x)+7 = sigma(x+7). See A063680 and indices resulting in primes are in A063679. %C A063681 The next term (a(7)) has 118 digits. - _Harvey P. Dale_, May 10 2014 %F A063681 2*37+7 = 3^4, so 37 is in the sequence. %t A063681 Select[(#-7)/2&/@(3^Range[2,250]),PrimeQ] (* _Harvey P. Dale_, May 10 2014 *) %Y A063681 Cf. A063679, A063680. %K A063681 nonn %O A063681 1,1 %A A063681 _Jud McCranie_, Jul 29 2001