A281265 Variation on betrothed numbers.

6160, 11697, 12220, 16005, 23500, 28917, 68908, 76245, 249424, 339825, 425500, 434784, 570405, 649990, 660825, 678376, 697851, 871585, 1017856, 1077336, 1238380, 1252216, 1340865, 1483785, 1568260, 1754536, 1823925, 1899261, 2067625, 2166136, 2362360, 2479065

Offset

1,1

Comments

Members of a pair (x,y) such that sigma(x) = sigma(y) = x + y - 1, where sigma = A000203.

The first time a pair ordered by its first element is not adjacent is x = 425500, y = 570405 which correspond to a(11) and a(13), respectively.

Links

Table of n, a(n) for n=1..32.

Formula

A007992 U A015630.

Example

sigma(6160) = sigma(11697) = 6160 + 11697 - 1 = 17856.

Maple

with(numtheory): P:=proc(q) local a, b, n; for n from 1 to q do
a:=sigma(n)-n+1; b:=sigma(a)-a+1; if b=n and a<>b then print(n);
fi; od; end: P(10^9);

Crossrefs

Cf. A000203, A005276, A007992, A015630.

Sequence in context: A203982 A204626 A318251 * A007992 A033288 A266586

Adjacent sequences: A281262 A281263 A281264 * A281266 A281267 A281268

Keyword

nonn,easy

Author

Paolo P. Lava, Apr 13 2017

Status

approved