OFFSET
1,2
COMMENTS
The sum of the distinct primes dividing 2n-1. - Emeric Deutsch, Mar 11 2005
EXAMPLE
a(23)=8 because 45=3^2*5 and 3+5=8.
MAPLE
with(numtheory): a:=proc(n) local b: b:=convert(factorset(2*n-1), list): add(b[j], j=1..nops(b)) end: seq(a(n), n=1..80); # Emeric Deutsch, Mar 11 2005
MATHEMATICA
Join[{0}, Total[Transpose[FactorInteger[#]][[1]]]&/@(2*Range[2, 80]-1)] (* Harvey P. Dale, Aug 05 2015 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Nov 20 2004
EXTENSIONS
More terms from Emeric Deutsch, Mar 11 2005
STATUS
approved