OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..1500
EXAMPLE
Aliquot parts of 6 are 1, 2, 3, which are all deficient numbers. Then sigma(1+2+3) = sigma(6) = 12 = usigma(6).
Aliquot parts of 68 are 1, 2, 4, 17, 34, twhich are all deficient numbers. Then sigma(1+2+4+17+34) = sigma(58) = 90 = usigma(68).
Aliquot parts of 828 are 1, 2, 3, 4, 6, 9, 12, 18, 23, 36, 46, 69, 92, 138, 207, 276, 414. Deficient numbers are 1, 2, 3, 4, 9, 23, 46, 69, 92 and 207. Then sigma(1+2+3+4+9+23+46+69+92+207) = sigma(456) = 1200 = usigma(828).
MAPLE
with(numtheory); P:=proc(q) local a, b, d, k, n; for n from 1 to q do
a:=sort([op(divisors(n))]); b:=0; d:=0;
for k from 1 to nops(a)-1 do if sigma(a[k])<2*a[k] then b:=b+a[k]; fi; od;
for k from 1 to nops(a) do if gcd(a[k], n/a[k])=1 then d:=d+a[k]; fi; od;
if sigma(b)=d then print(n); fi; od; end: P(10^9);
CROSSREFS
KEYWORD
nonn
AUTHOR
Paolo P. Lava, May 21 2015
STATUS
approved