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 A361977 #33 Apr 02 2023 11:28:18 %S A361977 3,5,7,13,13,19,23,23,29,31,31,37,43,43,47,53,53,59,61,61,67,73,73,79, %T A361977 83,83,89,89,89,97,101,103,109,109,113,113,113,113,127,131,131,139, %U A361977 139,139,149,151,151,157,157,163,167,167,173,179,181,181,181,191,193 %N A361977 a(n) is the largest prime p such that 2^p - 1 <= 10^n. %F A361977 a(n) = A151799(A067497(n)). - _Alois P. Heinz_, Apr 02 2023 %e A361977 a(5) = 13, 2^13 - 1 = 8192 < 10^5. %o A361977 (Python) %o A361977 from sympy import prevprime %o A361977 def A361977(n): return prevprime((10**n-1).bit_length()) # _Chai Wah Wu_, Apr 02 2023 %Y A361977 Cf. A000040, A000043, A000668, A011557, A067497, A151799. %K A361977 nonn,easy %O A361977 1,1 %A A361977 _Jack Braxton_, Apr 02 2023