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 A098102 #22 Feb 21 2025 16:45:33
%S A098102 1,3,15,63,1023,4095,65535,262143,4194303,268435455,1073741823,
%T A098102 68719476735,1099511627775,4398046511103,70368744177663,
%U A098102 4503599627370495,288230376151711743,1152921504606846975
%N A098102 a(n) = 2^(prime(n) - 1) - 1 where prime(n) is the n-th prime.
%e A098102 For n = 3; prime(3) = 5, a(3) = 2^(5-1) - 1 = 15.
%t A098102 Table[2^(Prime[n] - 1) - 1, {n, 20}]
%o A098102 (Magma) [2^(NthPrime(n)-1) - 1: n in [1..18]]; // _Jaroslav Krizek_, Jan 02 2015
%o A098102 (PARI) a(n) = 2^(prime(n)-1) - 1; \\ _Michel Marcus_, Jan 13 2023
%Y A098102 Cf. A097743, A000225.
%K A098102 nonn
%O A098102 1,2
%A A098102 _Parthasarathy Nambi_, Sep 22 2004
%E A098102 Edited and extended by _Robert G. Wilson v_, Sep 23 2004
%E A098102 Definition and example corrected by _Jaroslav Krizek_, Jan 02 2015
%E A098102 Name edited by _Michel Marcus_, Jan 13 2023