%I #18 Jan 13 2023 05:52:36

%S 1,3,15,63,1023,4095,65535,262143,4194303,268435455,1073741823,

%T 68719476735,1099511627775,4398046511103,70368744177663,

%U 4503599627370495,288230376151711743,1152921504606846975

%N a(n) = 2^(prime(n) - 1) - 1 where prime(n) is the n-th prime.

%e For n = 3; prime(3) = 5, a(3) = 2^(5-1) - 1 = 15.

%t Table[2^(Prime[n] - 1) - 1, {n, 20}]

%o (Magma)[2^(NthPrime(n)-1) - 1: n in [1..18]] // _Jaroslav Krizek_, Jan 02 2015

%o (PARI) a(n) = 2^(prime(n)-1) - 1; \\ _Michel Marcus_, Jan 13 2023

%Y Cf. A097743, A000225.

%K nonn

%O 1,2

%A _Parthasarathy Nambi_, Sep 22 2004

%E Edited and extended by _Robert G. Wilson v_, Sep 23 2004

%E Definition and example corrected by _Jaroslav Krizek_, Jan 02 2015

%E Name edited by _Michel Marcus_, Jan 13 2023