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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A297364 Numbers n such that f(n) > f(m) for all m < n, where f(n) = usigma(usigma(usigma(n)))/usigma(usigma(n)) and usigma(n) is the sum of unitary divisors of n (A034448). 0
 1, 2, 4, 10, 138, 163, 2511, 36943, 408403, 9869857, 11051023 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS 1 LINKS Imre Kátai and M. Wijsmuller, On the iterates of the sum of unitary divisors, Acta Mathematica Hungarica, Vol 79, No. 1-2 (1998), pp. 149-167. MATHEMATICA usigma[n_] := Block[{d = Divisors[n]}, Plus @@ Select[d, GCD[ #, n/# ] == 1 &]]; a = {}; k=1; rmax = 0; While[Length[a]<10, s = usigma[ k]; s1=usigma[s]; s2 = usigma[ s1]; r = s2/s1;  If[r > rmax, a = AppendTo[a, k]; rmax = r]; k++]; a CROSSREFS Cf. A034448. Sequence in context: A126140 A326967 A223851 * A327059 A012555 A012722 Adjacent sequences:  A297361 A297362 A297363 * A297365 A297366 A297367 KEYWORD nonn,more AUTHOR Amiram Eldar, Dec 29 2017 EXTENSIONS a(10) and a(11) from Robert G. Wilson v, Jan 12 2018 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 April 20 01:03 EDT 2021. Contains 343117 sequences. (Running on oeis4.)