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A145899 Numbers n such that sigma(x) = n has more solutions x than any smaller n. 6
1, 12, 24, 72, 168, 240, 336, 360, 504, 576, 720, 1440, 2880, 4320, 5760, 8640, 10080, 15120, 17280, 20160, 30240, 40320, 60480, 120960, 181440, 241920, 362880, 483840, 604800, 725760, 1088640, 1209600, 1451520, 2177280, 2419200, 2903040, 3628800 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Sequence A206027 has the number of solutions.

LINKS

Donovan Johnson, Table of n, a(n) for n = 1..100

EXAMPLE

sigma(m)=1 has only one solution: m=1.

sigma(m)=12 has two solutions, m=6 and m=11; 12 is the smallest number with more than one such solutions.

sigma(m)=24 has three solutions, m=14,m=15 and m=23; 24 is the smallest number with more than two such solutions.

sigma(m)=72 has five solutions, m=30, m=46, m=51, m=55 and m=71; 72 is the smallest number with more than three such solutions.

MATHEMATICA

t = DivisorSigma[1, Range[10^6]]; t2 = Sort[Tally[t]]; mn = 0; t3 = {}; Do[If[t2[[n]][[2]] > mn, mn = t2[[n]][[2]]; AppendTo[t3, t2[[n]][[1]]]], {n, Length[t2]}]; t3 (* T. D. Noe, Feb 03 2012 *)

PROG

(PARI) {m=3650000; v=vectorsmall(m); for(n=1, m, s=sigma(n); if(s<=m, v[s]++)); g=0; j=1; while(j<=m, if(v[j]<=g, j++, g=v[j]; print1(j, ", ")))} \\ Klaus Brockhaus, Oct 27 2008

CROSSREFS

Cf. A000203 (sum of divisors of n), A054973 (number of numbers whose divisors sum to n), A007368 (smallest k such that sigma(x) = k has exactly n solutions).

Cf. A206027.

Cf. Untouchable numbers (A005114), sigma-untouchable numbers (A007369) and highly touchable numbers (A238895).

Sequence in context: A227895 A001335 A206026 * A172011 A239635 A001041

Adjacent sequences:  A145896 A145897 A145898 * A145900 A145901 A145902

KEYWORD

nonn

AUTHOR

Douglas E. Iannucci, Oct 22 2008

EXTENSIONS

Extended beyond a(15) by Klaus Brockhaus, Oct 27 2008

STATUS

approved

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Last modified March 20 13:18 EDT 2019. Contains 321345 sequences. (Running on oeis4.)