A340720 Least positive number k such that sigma(k) = n * sigma(k+1).

14, 12, 180, 25908120

Offset

1,1

Links

Table of n, a(n) for n=1..4.

Example

  n | sigma(a(n)) | sigma(a(n)+1)
----+-------------+--------------
  1 |          24 |            24
  2 |          28 |            14
  3 |         546 |           182
  4 |   103680000 |      25920000

Prog

(PARI) {a(n) = my(k=1); while(sigma(k)!=n*sigma(k+1), k++); k}

Crossrefs

Cf. A002961, A080372, A163193, A217791, A340715.

Sequence in context: A305938 A206605 A004503 * A166041 A335170 A115019

Adjacent sequences: A340717 A340718 A340719 * A340721 A340722 A340723

Keyword

nonn,more,hard

Author

Seiichi Manyama, Jan 17 2021

Status

approved