OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..39
Wikipedia, Semiprime.
FORMULA
a(n) = 2^A135978(n) - 1. - Amiram Eldar, May 23 2021
MAPLE
A135976 := proc(n) local i;
i := 2^(ithprime(n))-1:
if (nops(numtheory[factorset](i)) = 2) then
RETURN (i)
fi: end: [ seq(A135976(n), n=1..26) ]; # Jani Melik, Feb 09 2011
MATHEMATICA
k = {}; Do[If[ ! PrimeQ[2^Prime[n] - 1], c = FactorInteger[2^Prime[n] - 1]; d = Length[c]; If[d == 2, AppendTo[k, 2^Prime[n] - 1]]], {n, 1, 40}]; k
PROG
(PARI) forprime(p=1, 1e2, if(bigomega(2^p-1)==2, print1(2^p-1, ", "))) \\ Felix Fröhlich, Aug 12 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Artur Jasinski, Dec 09 2007
STATUS
approved