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 A220851 #8 Dec 23 2012 23:43:23 %S A220851 2,3,4,6,8,10,14,17,21,26,32,39,48,57,71,85,101,121,144,171,200,232, %T A220851 272,314,363,419,483,553,637,727,829,944,1073,1217,1378,1560,1758, %U A220851 1975,2225,2498,2799,3130,3498,3909,4357,4848,5394,5996,6651,7374,8163 %N A220851 a(n+1) is equal to a(n) plus the number of primes between a(n) and 2*a(n) exclusively. %H A220851 Robert G. Wilson v, <a href="/A220851/b220851.txt">Table of n, a(n) for n = 1..558</a> %e A220851 a(6) = the number of primes between a(5) and 2*a(5) plus a(5) = the number of primes ]8, 16[ + 8 = 2 + 8 = 10. %t A220851 f[n_] := PrimePi[2n - 1] - PrimePi[n]; NestList[# + f@# &, 2, 50] %Y A220851 Cf. A060715, A220850, inspired by A084140. %K A220851 easy,nonn %O A220851 1,1 %A A220851 _Robert G. Wilson v_, Dec 22 2012