OFFSET
1,3
COMMENTS
Number of arithmetic numbers <= n, cf. A003601; partial sums of A245656. - Reinhard Zumkeller, Jul 28 2014
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
Wikipedia, Arithmetic number
FORMULA
a(n)=Card(k: 1<=k<=n : sigma(k) == 0 (mod tau(k) ) : lim n -> infinity a(n)/n=C=0, 8...
MATHEMATICA
Accumulate[Table[If[Divisible[DivisorSigma[1, n], DivisorSigma[0, n]], 1, 0], {n, 80}]] (* Harvey P. Dale, Oct 06 2020 *)
PROG
(PARI) for(n=1, 150, print1(sum(i=1, n, if(sigma(i)%numdiv(i), 0, 1)), ", "))
(Haskell)
a069928 n = a069928_list !! (n-1)
a069928_list = scanl1 (+) a245656_list
-- Reinhard Zumkeller, Jul 28 2014
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, May 05 2002
STATUS
approved