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 A135630 #13 Sep 08 2022 08:45:32
%S A135630 0,1,7,31,511,2047,32767,131071,2097151,134217727,536870911,
%T A135630 34359738367,549755813887,2199023255551,35184372088831,
%U A135630 2251799813685247,144115188075855871,576460752303423487,36893488147419103231,590295810358705651711
%N A135630 2^(prime(n) - 2) - 1.
%H A135630 Vincenzo Librandi, <a href="/A135630/b135630.txt">Table of n, a(n) for n = 1..200</a>
%F A135630 a(n) = 2^(A000040(n)-2) - 1 = 2^(A040976(n)) - 1 = (2^A000040(n)/4) - 1 = (A061286(n)/2) - 1.
%e A135630 a(4)=31 because the 4th prime number is 7 and 7-2=5 and 2^5=32 and 32-1=31.
%t A135630 Table[2^(Prime[n]-2)-1,{n,20}] (* _Harvey P. Dale_, Feb 25 2011 *)
%o A135630 (Magma) [2^(NthPrime(n)-2)-1: n in [1..30]]; // _Vincenzo Librandi_, Sep 06 2014
%Y A135630 Cf. A000040, A040976, A061286.
%K A135630 easy,nonn
%O A135630 1,3
%A A135630 _Omar E. Pol_, Mar 01 2008
%E A135630 More terms from _Harvey P. Dale_, Feb 25 2011