1,1

Also, twice perfect numbers, if there are no odd perfect numbers.

If there are no odd perfect numbers, essentially the same as A065125. - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 23 2008

O. E. Pol, Determinacion geometrica de los numeros primos y perfectos.

a(n) = A000668(n)*((A000668(n)+1). Also, a(n) = 2*A000396(n), if there are no odd perfect numbers.

a(3)=992 because the third Mersenne prime A000668(3) is 31 and 31*(31+1) = 31*32 = 992.

Sequence in context: A081756 A027147 A095724 this_sequence A123983 A071270 A051877

Adjacent sequences: A139253 A139254 A139255 this_sequence A139257 A139258 A139259

nonn

Omar E. Pol (info(AT)polprimos.com), Apr 22 2008