OFFSET
1,2
COMMENTS
a(13) and a(14) have 157 and 183 digits respectively. - R. J. Mathar, Jan 07 2008
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.
Indices of even hexagonal numbers (A014635) that are also even perfect numbers. - Omar E. Pol, Jan 11 2009
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..18
Omar E. Pol, Determinacion geometrica de los numeros primos y perfectos [From Omar E. Pol, Jan 11 2009]
FORMULA
a(n) = A061652(n)/2.
a(n) = 2^(A000043(n)-2). - Omar E. Pol, Mar 01 2008
a(n) = A032742(A061652(n)). Also, a(n) = A032742(A019279(n)), if there are no odd superperfect numbers.
a(n) = Sum_{x=1..n-th superperfect number} x*(-1)^x. - Juri-Stepan Gerasimov, Jul 21 2009
EXAMPLE
a(5) = 2048 because the 5th even superperfect number is 4096 and 4096/2 = 2048.
MAPLE
MATHEMATICA
With[{max = 12}, 2^(MersennePrimeExponent[Range[max]] - 2)] (* Amiram Eldar, Oct 21 2024 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Omar E. Pol, Nov 07 2007, Apr 23 2008
EXTENSIONS
More terms from R. J. Mathar, Jan 07 2008
STATUS
approved