A133067 Perfect numbers divided by 2, minus 1.

2, 13, 247, 4063, 16775167, 4294934527, 68719345663, 1152921504069976063, 1329227995784915872327346307976921087, 95780971304118053647396689042151819065498660774084607

Offset: 1

Author

Omar E. Pol, Nov 07 2007

Keywords

• nonn

Examples

			a(3)=247 because the 3rd perfect number is 496 and 496/2 is 248. a(3)=248-1.
		

Crossrefs

Cf. A000396, A133028.

Programs

Mathematica

p = Select[2^Range[400] - 1, PrimeQ]; p*(p+1)/4 - 1 (* Vladimir Joseph Stephan Orlovsky, Feb 02 2012 *)

Formula

a(n)=(A000396(n)/2)-1.