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 A242083 #31 May 21 2025 18:42:29
%S A242083 4,18,210,2058,175098,1586130,129009090,1161737178,94134790218,
%T A242083 68629840493970,617671248800298,450283768452043890,
%U A242083 36472994178147530850,328256958598444055418,26588814218220014932458,19383245658672820642055730
%N A242083 a(n) = 3^p - 2^p - 1, where p is prime(n).
%C A242083 For p>3, all terms are divisible by 42.
%H A242083 Vincenzo Librandi, <a href="/A242083/b242083.txt">Table of n, a(n) for n = 1..320</a>
%F A242083 a(n) = abs(A083321(A000040(n))). - _Michel Marcus_, May 05 2014
%t A242083 Table[(3^Prime[n] - 2^Prime[n] - 1), {n, 1, 30}]
%t A242083 3^#-2^#-1&/@Prime[Range[20]] (* _Harvey P. Dale_, Aug 05 2016 *)
%o A242083 (Magma) [3^p-2^p-1: p in PrimesUpTo(60)];
%o A242083 (PARI) a(n) = my(p = prime(n)); 3^p-2^p-1; \\ _Michel Marcus_, May 05 2014
%o A242083 (Sage) [3^p-2^p-1 for p in primes(60)] # _Bruno Berselli_, May 12 2014
%Y A242083 Cf. A000040, A083321, A204768.
%K A242083 nonn,easy
%O A242083 1,1
%A A242083 _Vincenzo Librandi_, May 04 2014