A007609 - OEIS

A007609

Values taken by the sigma function A000203, listed with multiplicity and in ascending order.

1, 3, 4, 6, 7, 8, 12, 12, 13, 14, 15, 18, 18, 20, 24, 24, 24, 28, 30, 31, 31, 32, 32, 36, 38, 39, 40, 42, 42, 42, 44, 48, 48, 48, 54, 54, 56, 56, 57, 60, 60, 60, 62, 63, 68, 72, 72, 72, 72, 72, 74, 78, 80, 80, 84, 84, 84, 90, 90, 90, 91, 93, 96, 96, 96, 96, 98, 98

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OFFSET

1,2

COMMENTS

A175192(a(n)) = 1, A054973(a(n)) >= 1. - Jaroslav Krizek, Mar 01 2010

a(n) is the median of the values of A000203(m) from m=1 to m=2n-1. (This needs confirmation as it relies on the assumption that A000203(n) is always bigger than the median of the values A000203(x) from x=1 to x=n.) - Chayim Lowen, May 27 2015

LINKS

T. D. Noe, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = sigma(A085790(n)). - Jinyuan Wang, Apr 15 2020

MAPLE

sort(select(`<=`, map(numtheory:-sigma, [$1..1000]), 1001)); # Robert Israel, Jun 04 2015

MATHEMATICA

terms = 68; ClearAll[t]; t[k_] := t[k] = Sort[ Table[ DivisorSigma[1, n], {n, 1, k*terms}]][[1 ;; terms]]; t[k = 2]; While[t[k] != t[k-1], k++]; t[k] (* Jean-François Alcover, Nov 21 2012 *)

With[{nn=80}, Take[Sort[DivisorSigma[1, Range[nn*100]]], nn]] (* Harvey P. Dale, Mar 09 2016 *)

PROG

(PARI) list(lim)=select(k->k<=lim, Set(apply(sigma, [1..lim\1]))) \\ Charles R Greathouse IV, Mar 09 2014

CROSSREFS

Cf. A000203, A002191 (duplicates removed), A007368, A085790.

Sequence in context: A191775 A047515 A066650 * A285703 A002191 A108348

Adjacent sequences: A007606 A007607 A007608 * A007610 A007611 A007612

KEYWORD

nonn,easy,nice

AUTHOR

Walter Nissen

STATUS

approved