A376831 Numbers k such that sigma(k + sigma(k)) = sigma(k) + sigma(sigma(k)), where sigma = A000203.

1986, 58920, 88092, 111276, 201588, 662160, 1103076, 1573536, 1671056, 1887900, 3172434, 4507152, 4575124, 8105188, 10971936, 42273728, 56886840

Offset

1,1

Links

Table of n, a(n) for n=1..17.

Example

a(3) =  88092 is a term because sigma(88092) = 222768, sigma(222768) = 812448 and sigma(88092 + 222768) = sigma(310860) = 1035216 = 222768 + 812448.

Maple

filter:= proc(k) uses numtheory; local s;
 s:= sigma(k);
 sigma(k+s) = s + sigma(s)
end proc:
select(filter, [$1..10^7]);

Crossrefs

Cf. A000203, A376830, A376843, A376844, A376848, A376849, A376851.

Sequence in context: A107527 A034228 A028516 * A206363 A233712 A223366

Adjacent sequences: A376828 A376829 A376830 * A376832 A376833 A376834

Keyword

nonn,more

Author

Robert Israel, Oct 05 2024

Status

approved