A308098 - OEIS

A308098

Numbers m such that sequence of their values of sigma(m) corresponds to sequence of unique values of function sigma(n) for n >= 1 in increasing order (A007370).

1, 2, 3, 5, 4, 7, 9, 13, 8, 19, 12, 29, 22, 37, 18, 27, 43, 49, 61, 32, 67, 73, 45, 36, 50, 101, 109, 91, 81, 64, 121, 137, 149, 157, 133, 106, 163, 98, 173, 129, 169, 193, 72, 197, 199, 134, 211, 100, 146, 229, 241, 128, 217, 257, 171, 148, 277, 281, 283, 219

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OFFSET

1,2

COMMENTS

A211656 is the sorted version of this sequence.

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

Index entries for sequences related to sigma(n)

FORMULA

A000203(a(n)) = A007370(n) for all n.

EXAMPLE

a(6) = 7 because A007370(6) = 8 and there is only one solution of equation sigma(x) = 8 for x = 7.

MATHEMATICA

m = 500; v = Table[0, {m}]; Do[s = DivisorSigma[1, k]; If[s <= m , v[[s]] = If[ v[[s]] == 0, k, -1]], {k, 1, m - 1}]; Select[v, # > 0 &] (* Amiram Eldar, Jul 04 2019 *)

PROG

(Magma) [[m: m in [1..1000] | SumOfDivisors(m) eq n]: n in [1..100] | #[#[m]: m in [1..1000] | SumOfDivisors(m) eq n] eq 1]

CROSSREFS

Cf. A000203, A007370, A211656, A211657.

Sequence in context: A140140 A242693 A119474 * A029654 A297769 A213921

Adjacent sequences: A308095 A308096 A308097 * A308099 A308100 A308101

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, May 12 2019

STATUS

approved