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A064535 a(n) = (2^prime(n)-2)/prime(n); a(0) = 0 by convention.

%I A064535 #38 Sep 08 2022 08:45:04
%S A064535 0,1,2,6,18,186,630,7710,27594,364722,18512790,69273666,3714566310,
%T A064535 53634713550,204560302842,2994414645858,169947155749830,
%U A064535 9770521225481754,37800705069076950,2202596307308603178,33256101992039755026,129379903640264252430
%N A064535 a(n) = (2^prime(n)-2)/prime(n); a(0) = 0 by convention.
%C A064535 As a corollary to Fermat's little theorem, (2^p - 2)/p is always an integer for p prime. - _Alonso del Arte_, May 04 2013
%H A064535 Harry J. Smith, <a href="/A064535/b064535.txt">Table of n, a(n) for n = 0..100</a>
%F A064535 a(n) = A001037(prime(n)) for n >= 1. - _Hilko Koning_, Sep 10 2018
%F A064535 a(n) = 2*A007663(n) for n > 1. - _Jeppe Stig Nielsen_, May 16 2021
%e A064535 a(3) = 6, because prime(3) = 5, and (2^5 - 2)/5 = 30/5 = 6.
%e A064535 a(4) = 18, because prime(4) = 7, and (2^7  - 2)/7 = 126/7 = 18.
%p A064535 A064535 := proc(n) ( 2^ithprime(n) - 2 )/ithprime(n); end;
%t A064535 Table[(2^Prime[n] - 2)/Prime[n], {n, 50}] (* _Alonso del Arte_, Apr 28 2013 *)
%o A064535 (PARI) { for (n=0, 100, if (n, a=(2^prime(n) - 2)/prime(n), a=0); write("b064535.txt", n, " ", a) ) } \\ _Harry J. Smith_, Sep 17 2009
%o A064535 (Magma) [0] cat [(2^NthPrime(n)-2)/NthPrime(n): n in [1..25]]; // _Vincenzo Librandi_, Sep 14 2018
%Y A064535 Cf. A007663, A056743, A225101 (superset).
%K A064535 nonn
%O A064535 0,3
%A A064535 _Shane Findley_, Oct 09 2001