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A286322 Totient highly abundant numbers that are composite. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified January 18 11:57 EST 2022. Contains 350455 sequences. (Running on oeis4.)