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

14, 12, 180, 25908120

Offset: 1

Author

Seiichi Manyama, Jan 17 2021

Keywords

• nonn
• more
• hard

Examples

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

Crossrefs

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

Programs

PARI

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