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 A134708 #18 Oct 21 2024 04:35:49
%S A134708 1,2,8,32,2048,32768,131072,536870912,576460752303423488,
%T A134708 154742504910672534362390528,40564819207303340847894502572032,
%U A134708 42535295865117307932921825928971026432
%N A134708 Even superperfect numbers divided by 2.
%C A134708 a(13) and a(14) have 157 and 183 digits respectively. - _R. J. Mathar_, Jan 07 2008
%C A134708 Largest proper divisor of n-th even superperfect number A061652(n). Also, largest proper divisor of n-th superperfect number A019279(n), if there are no odd superperfect numbers.
%C A134708 Indices of even hexagonal numbers (A014635) that are also even perfect numbers. - _Omar E. Pol_, Jan 11 2009
%H A134708 Amiram Eldar, <a href="/A134708/b134708.txt">Table of n, a(n) for n = 1..18</a>
%H A134708 Omar E. Pol, <a href="http://www.polprimos.com">Determinacion geometrica de los numeros primos y perfectos</a> [From _Omar E. Pol_, Jan 11 2009]
%F A134708 a(n) = A061652(n)/2.
%F A134708 a(n) = 2^(A000043(n)-2). - _Omar E. Pol_, Mar 01 2008
%F A134708 a(n) = A032742(A061652(n)). Also, a(n) = A032742(A019279(n)), if there are no odd superperfect numbers.
%F A134708 a(n) = Sum_{x=1..n-th superperfect number} x*(-1)^x. - _Juri-Stepan Gerasimov_, Jul 21 2009
%e A134708 a(5) = 2048 because the 5th even superperfect number is 4096 and 4096/2 = 2048.
%p A134708 A000043 := proc(n) op(n,[2, 3, 5, 7, 13, 17, 19, 31, 61, 89, 107, 127, 521, 607, 1279, 2203, 2281, 3217, 4253, 4423, 9689, 9941, 11213]) ; end: A061652 := proc(n) 2^(A000043(n)-1) ; end: A134708 := proc(n) A061652(n)/2 ; end: seq(A134708(n),n=1..14) ; # _R. J. Mathar_, Jan 07 2008
%t A134708 With[{max = 12}, 2^(MersennePrimeExponent[Range[max]] - 2)] (* _Amiram Eldar_, Oct 21 2024 *)
%Y A134708 Cf. A019279, A061652, A133028.
%Y A134708 Cf. A000043.
%Y A134708 Cf. A032742, A138882, A139248.
%Y A134708 Cf. A000217, A000396, A014635. - _Omar E. Pol_, Jan 11 2009
%K A134708 nonn
%O A134708 1,2
%A A134708 _Omar E. Pol_, Nov 07 2007, Apr 23 2008
%E A134708 More terms from _R. J. Mathar_, Jan 07 2008