cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A238765 Numbers k such that if x = Sum_{j|k, j

Original entry on oeis.org

198, 608, 11322, 15450, 17874, 20826, 33894, 41022, 56608, 1259910, 1764414, 3055150, 565344850, 579667086, 907521650
Offset: 1

Views

Author

Paolo P. Lava, Mar 05 2014

Keywords

Comments

A066218 is a subsequence. It lists the fixed points of the transform n -> Sum_{j|n, j

Examples

			Aliquot divisors of 15450 are 1, 2, 3, 5, 6, 10, 15, 25, 30, 50, 75, 103, 150, 206, 309, 515, 618, 1030, 1545, 2575, 3090, 5150, 7725. Their respective sigma(k)-k are 0, 1, 1, 1, 6, 8, 9, 6, 42, 43, 49, 1, 222, 106, 107, 109, 630, 842, 951, 649, 4398, 4522, 5171 and their sum is equal to 17874.
Aliquot divisors of 17874 are 1, 2, 3, 6, 9, 18, 27, 54, 331, 662, 993, 1986, 2979, 5958, 8937. Their respective sigma(k)-k are 0, 1, 1, 6, 4, 21, 13, 66, 1, 334, 335, 1998, 1337, 6990, 4343 and their sum is equal to 15450.

Crossrefs

Cf. A000203, A066218.

Programs

  • Maple
    with(numtheory); P:=proc(q) local a,b,c,i,n;
for n from 1 to q do a:=sort([op(divisors(n))]); b:=0;
for i from 1 to nops(a)-1 do b:=b+sigma(a[i])-a[i]; od;
a:=sort([op(divisors(b))]); c:=0;
for i from 1 to nops(a)-1 do c:=c+sigma(a[i])-a[i]; od;
if n=c then print(n); fi; od; end: P(10^6);

Extensions

a(13)-a(15) from Michel Marcus, Mar 07 2014

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