OFFSET
1,1
EXAMPLE
Aliquot divisors of 4240 are 1, 2, 4, 5, 8, 10, 16, 20, 40, 53, 80, 106, 212, 265, 424, 530, 848, 1060, 2120 and the abundant numbers are 20, 40, 80, 1060, 2120. Their sum is 3320 and sigma(3320) - 3320 = 4240.
MAPLE
with(numtheory); P:=proc(q) local a, b, k, n;
for n from 1 to q do a:=sort([op(divisors(n))]); b:=0;
for k from 1 to nops(a)-1 do if sigma(a[k])>2*a[k]
then b:=b+a[k]; fi; od; if sigma(b)-b=n
then print(n); fi; od; end: P(10^9);
MATHEMATICA
seqQ[n_] := Module[{s = Total@Select[Most[Divisors[n]], DivisorSigma[1, #] > 2# &]}, s>0 && DivisorSigma[1, s] - s == n]; Select[Range[10^6], seqQ] (* Amiram Eldar, Mar 20 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Paolo P. Lava, Feb 10 2015
EXTENSIONS
a(3) inserted and a(11)-a(28) added by Amiram Eldar, Mar 20 2019
STATUS
approved