A340715 Least positive number k such that sigma(k+1) = n * sigma(k).

14, 5, 1, 37033919, 14182439039

Offset

1,1

Links

Table of n, a(n) for n=1..5.

Example

  n | sigma(a(n)) | sigma(a(n)+1)
----+-------------+--------------
  1 |          24 |            24
  2 |           6 |            12
  3 |           1 |             3
  4 |    39940992 |     159763968
  5 | 14182439040 |   70912195200

Mathematica

k = 1; n = 1; Print[While[DivisorSigma[1, k + 1] != n*DivisorSigma[1, k], k; k k+]; k] (* Robert P. P. McKone, Jan 17 2021 *)

Prog

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

Crossrefs

Cf. A000203, A002961, A058072, A067081, A077087, A080371, A340713, A340720.

Sequence in context: A322776 A040186 A124600 * A344046 A084676 A180848

Adjacent sequences: A340712 A340713 A340714 * A340716 A340717 A340718

Keyword

nonn,hard,more

Author

Seiichi Manyama, Jan 17 2021

Status

approved