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 A108301 #10 Dec 15 2017 17:36:49
%S A108301 3,5,8,14,26,59,89,167,377,734,1376,2741,5624,11120,22166,44222,88262,
%T A108301 176180,353042,707648,1419974,2836751,5679620,11365592,22723865,
%U A108301 45445442,90899234,181828850
%N A108301 Digital sum of the Fermat number 2^(2^n) + 1.
%C A108301 a(0), a(1), a(5), a(6), a(7) and a(11) are primes. Are there any more?
%F A108301 a(n) = ~4.5*A057755. - _Robert G. Wilson v_, Jul 02 2005
%e A108301 a(5)=59 because 2^(2^5) + 1 = 4294967297 and the sum of those decimal digits is 59.
%p A108301 a:=proc(n) local nn, z: nn:=convert(2^(2^n)+1,base,10): z:=nops(nn): add(nn[j],j=1..z) end: seq(a(n),n=0..22); # _Emeric Deutsch_
%t A108301 f[n_] := Plus @@ IntegerDigits[2^(2^n)] + 1; Table[ f[n], {n, 0, 27}] (* _Robert G. Wilson v_, Jul 02 2005 *)
%Y A108301 Cf. A000215.
%K A108301 base,nonn
%O A108301 0,1
%A A108301 _Jason Earls_, Jun 29 2005
%E A108301 More terms from _Emeric Deutsch_ and _Robert G. Wilson v_, Jul 02 2005