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 A132931 #7 Aug 25 2023 16:24:43
%S A132931 3,37,3731,3731127,37311278191,37311278191131071,
%T A132931 37311278191131071524287,373112781911310715242872147483647,
%U A132931 3731127819113107152428721474836472305843009213693951
%N A132931 Concatenation of first n Mersenne primes.
%H A132931 C. K. Caldwell, <a href="http://www.utm.edu/research/primes/mersenne/index.html">Mersenne Primes</a>.
%H A132931 Omar E. Pol, <a href="http://www.polprimos.com">Determinacion geometrica de los numeros primos y perfectos</a>.
%t A132931 Module[{nn=15,mp},mp=2^MersennePrimeExponent[Range[nn]]-1;Table[FromDigits[Flatten[ IntegerDigits/@Take[mp,n]]],{n,nn}]] (* _Harvey P. Dale_, Aug 25 2023 *)
%Y A132931 Mersenne primes: A000668. Cf. A007908, A019518, A059996, A078795, A089933.
%K A132931 easy,nonn,base
%O A132931 1,1
%A A132931 _Omar E. Pol_, Sep 05 2007