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

Author

Paolo P. Lava, Apr 13 2017

Keywords

• nonn
• easy

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.

Examples

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

Crossrefs

Cf. A000203, A005276, A007992, A015630.

Programs

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);

Formula

A007992 U A015630.