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A340715 Least positive number k such that sigma(k+1) = n * sigma(k). 2
14, 5, 1, 37033919, 14182439039 (list; graph; refs; listen; history; text; internal format)
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

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Last modified August 10 03:38 EDT 2022. Contains 356029 sequences. (Running on oeis4.)