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 A117293 #18 Oct 22 2024 05:43:18 %S A117293 11,111,11111,1111111,1111111111111,11111111111111111, %T A117293 1111111111111111111,1111111111111111111111111111111, %U A117293 1111111111111111111111111111111111111111111111111111111111111 %N A117293 Mersenne primes written in binary. %C A117293 The number of bits in a(n) is equal to A000043(n). - _Omar E. Pol_, Feb 22 2008 %H A117293 Amiram Eldar, <a href="/A117293/b117293.txt">Table of n, a(n) for n = 1..14</a> %H A117293 Wikipedia, <a href="http://en.wikipedia.org/wiki/Mersenne_prime">Mersenne prime</a>. %F A117293 a(n) = A007088(A000668(n)). - _Amiram Eldar_, Oct 22 2024 %e A117293 The third Mersenne prime is 31, i.e., 11111 in binary. %t A117293 Map[(10^# - 1)/9 &, MersennePrimeExponent[Range[9]]] (* _Amiram Eldar_, Oct 22 2024 *) %o A117293 (PARI) apply(p->fromdigits(binary(p)), select(isprime, vector(20,n,2^prime(n)-1))) \\ _Charles R Greathouse IV_, Sep 14 2016 %Y A117293 Cf. A000043, A000668, A007088. %K A117293 base,nonn %O A117293 1,1 %A A117293 _Jacob Vecht_, Apr 23 2006