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 A331204 #7 Jan 12 2020 10:48:39 %S A331204 1,2,3,39,5,7,8,47,9,13,14,27,14,23,17,447,17,23,20,31,23,27,34,39,31, %T A331204 31,29,31,43,41,32,191,40,43,49,59,38,41,42,255,64,43,65,331,48,59,62, %U A331204 111,52,79,53,91,55,75,61,199,71,65,86,99,65,127,74 %N A331204 Least m > n such that 2^m - 2^n + 1 is prime. %C A331204 If it exists, a(63) > 10000. %e A331204 a(0) = 1: 2^1 - 2^0 + 1 = 2 = A331205(0) is prime, %e A331204 a(1) = 2: 2^2 - 2^1 + 1 = 3 = A331205(1) is prime, %e A331204 a(2) = 3: 2^3 - 2^2 + 1 = 5 = A331205(2) is prime, %e A331204 a(3) = 39: 2^39 - 2^3 + 1 = 549755813881 = A331205(3) is prime, whereas all smaller values of m give composite sums: 9, 25, 57, 121, 249, 505, ..., 274877906937. %o A331204 (PARI) for(n=0,62, for(m=n+1,oo, k=2^m-2^n+1; if(isprime(k), print1(m,", "); break))) %Y A331204 Cf. A181692, A331205 (corresponding primes). %K A331204 nonn,hard %O A331204 0,2 %A A331204 _Hugo Pfoertner_, Jan 12 2020