OFFSET
1,3
COMMENTS
sigma(n) = sum of divisors of n, A000203.
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
FORMULA
EXAMPLE
a(14) = 6 because sigma(14) = 24 and the 6 even divisors are {2, 4, 6, 8, 12, 24}.
MATHEMATICA
a[n_] := Block[{d = Divisors[DivisorSigma[1, n]]}, Count[EvenQ[d], True]]; Table[a[n], {n, 80}]
PROG
(PARI) a(n)=n=sigma(n); if(n%2, 0, numdiv(n/2)) \\ Charles R Greathouse IV, Jul 30 2011
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Michel Lagneau, Jul 23 2011
STATUS
approved