OFFSET
1,1
COMMENTS
Includes (m+1)/2 for m in A000668. By Mihailescu's theorem, these are the only powers of 2 in the sequence. - Robert Israel, Feb 09 2017
LINKS
Ivan Neretin, Table of n, a(n) for n = 1..10000
MAPLE
pp:= n -> nops(ifactors(n)[2])=1:
select(n-> pp(n) and pp(numtheory:-sigma(n)), [$1..10^6]); # Robert Israel, Feb 09 2017
MATHEMATICA
Select[Range[600000], PrimePowerQ[#] && PrimePowerQ[DivisorSigma[1, #]] &] (* Ivan Neretin, Feb 08 2017 *)
PROG
(PARI) for(n=1, 100000, if(omega(n)*omega(sigma(n)) == 1, print1(n, ", ")))
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, May 27 2002
EXTENSIONS
Edited by Robert G. Wilson v and David Wasserman, May 30 2002
STATUS
approved