The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A289132 Indices of records in A063974. 6
 1, 12, 24, 60, 72, 216, 240, 720, 1440, 2160, 2880, 4320, 8640, 10080, 12960, 17280, 20160, 25920, 30240, 40320, 43200, 51840, 60480, 90720, 103680, 120960, 181440, 241920, 302400, 362880, 483840, 604800, 725760, 1088640, 1209600, 1451520, 1814400, 2419200 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that usigma(x) = n has more solutions x than any smaller n, where usigma(x) is the sum of unitary divisors of x (A034448). The unitary version of A145899. The corresponding number of solutions for each term is: 1, 2, 3, 4, 6, 7, 11, 18, 27, 30, 32, 48, 63, 65, 71, 88, 89, 102, 121, 122, 131, 144, 188, 190, 203, 262, 313, 364, 377, 472, 483, 584, 668, 725, 810, 928, 1076, 1138. Is this a subsequence of A025487? - David A. Corneth, Jun 25 2017 LINKS Amiram Eldar, Table of n, a(n) for n = 1..53 EXAMPLE There are 3 solutions to usigma(x) = 24: usigma(14) = usigma(15) = usigma(23) = 24. For all m < 24, there are 2 or fewer solutions to usigma(x) = m, thus 24 is in the sequence. MATHEMATICA usigma[n_] := Block[{d = Divisors[n]}, Plus @@ Select[d, GCD[#, n/#] == 1 &]]; t = Map[usigma, Range[10^7]]; 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 (* after T. D. Noe at A145899 *) CROSSREFS Cf. A025487, A034448, A063974, A145899. Sequence in context: A346865 A123980 A097704 * A348716 A098585 A087105 Adjacent sequences:  A289129 A289130 A289131 * A289133 A289134 A289135 KEYWORD nonn AUTHOR Amiram Eldar, Jun 25 2017 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 9 07:53 EST 2021. Contains 349627 sequences. (Running on oeis4.)