OFFSET
1,4
COMMENTS
Sum of divisors of n smaller than n that are deficient numbers (in A005100).
LINKS
FORMULA
EXAMPLE
Proper divisors of 90 are: 1, 2, 3, 5, 6, 9, 10, 15, 18, 30, 45. Of these 1, 2, 3, 5, 9, 10, 15 and 45 are in A005100, thus a(90) = 1+2+3+5+9+10+15+45 = 90.
MATHEMATICA
a[n_] := DivisorSum[n, # &, # < n && DivisorSigma[1, #] < 2*# &]; Array[a, 100] (* Amiram Eldar, Mar 14 2024 *)
PROG
(PARI) A294886(n) = sumdiv(n, d, (d<n)*(sigma(d)<(2*d))*d);
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Nov 14 2017
STATUS
approved