A361977 - OEIS

%I #33 Apr 02 2023 11:28:18

%S 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 83,83,89,89,89,97,101,103,109,109,113,113,113,113,127,131,131,139,

%U 139,139,149,151,151,157,157,163,167,167,173,179,181,181,181,191,193

%N a(n) is the largest prime p such that 2^p - 1 <= 10^n.

%F a(n) = A151799(A067497(n)). - _Alois P. Heinz_, Apr 02 2023

%e a(5) = 13, 2^13 - 1 = 8192 < 10^5.

%o (Python)

%o from sympy import prevprime

%o def A361977(n): return prevprime((10**n-1).bit_length()) # _Chai Wah Wu_, Apr 02 2023

%Y Cf. A000040, A000043, A000668, A011557, A067497, A151799.

%K nonn,easy

%O 1,1

%A _Jack Braxton_, Apr 02 2023