A286322 - OEIS

A286322

Totient highly abundant numbers that are composite.

4, 9, 221, 289, 697, 1819, 2329, 4369, 4913, 6439, 18769, 21331, 35209, 66049, 128881, 184783, 197143, 258121, 281929, 516961, 739903, 971203, 1762249, 1942663, 2070721, 2898703, 2952673, 3820819, 4142881, 5550943, 5869681, 8288641, 16230481, 16773619

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OFFSET

1,1

COMMENTS

Intersection of A002808 and A286267.

Of the 65 terms below 10^9, only 2 have more than 2 prime factors: a(9) = 17^3 and a(36) = 257^3, and 11 are prime powers: a(1) = 2^2, a(2) = 3^2, a(4) = 17^2, a(9) = 17^3, a(11) = 137^2, a(14) = 257^2, a(15) = 359^2, a(20) = 719^2, a(25) = 1439^2, a(32) = 2879^2, and a(36) = 257^3.

LINKS

Amiram Eldar and Giovanni Resta, Table of n, a(n) for n = 1..93 (terms < 5*10^10, first 65 terms from Amiram Eldar)

MATHEMATICA

sumTot[n_] := Plus @@ FixedPointList[ EulerPhi@ # &, n] - 1; a={}; smax=0; For[k=1, k<300000, k++; s=sumTot[k]; If[s>smax, smax=s; If[!PrimeQ[k], a=AppendTo[a, k]]]]; a

CROSSREFS

Cf. A002808, A286267.

Sequence in context: A006280 A290158 A202463 * A318615 A030074 A335723

Adjacent sequences: A286319 A286320 A286321 * A286323 A286324 A286325

KEYWORD

nonn

AUTHOR

Amiram Eldar, May 07 2017

STATUS

approved