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A340715
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Least positive number k such that sigma(k+1) = n * sigma(k).
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2
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OFFSET
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1,1
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LINKS
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Table of n, a(n) for n=1..5.
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EXAMPLE
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n | sigma(a(n)) | sigma(a(n)+1)
----+-------------+--------------
1 | 24 | 24
2 | 6 | 12
3 | 1 | 3
4 | 39940992 | 159763968
5 | 14182439040 | 70912195200
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MATHEMATICA
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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 *)
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PROG
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(PARI) {a(n) = my(k=1); while(sigma(k+1)!=n*sigma(k), k++); k}
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CROSSREFS
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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
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KEYWORD
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nonn,hard,more
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AUTHOR
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Seiichi Manyama, Jan 17 2021
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STATUS
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approved
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