A015810 k is the first integer such that phi(k+n) | sigma(k)+n.

1, 1, 10, 1, 6, 1, 10, 1, 7, 16, 5, 1, 3, 2, 10, 1, 14, 1, 10

Offset

0,3

Comments

a(20)=12, a(21)=98, a(22)=26, a(23)=1, a(24)=15, a(25)=8. - Jud McCranie, Jan 19 2020

a(19) > 10^13, if it exists. - Giovanni Resta, Jan 23 2020

Links

Table of n, a(n) for n=0..18.

Example

For n=6, a(6)=10 because phi(10+6)=8 which divides sigma(10)+6=24, and k=10 is the smallest integer with that property. - Jud McCranie, Jan 19 2020

Prog

(PARI) a(n) = k=1; while ((sigma(k)+n) % eulerphi(k+n), k++); k; \\ Michel Marcus, Feb 03 2014

Crossrefs

Sequence in context: A131790 A173330 A321097 * A010183 A242553 A113513

Adjacent sequences: A015807 A015808 A015809 * A015811 A015812 A015813

Keyword

nonn,more,hard

Author

Robert G. Wilson v

Status

approved