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A230214 Nonprime terms in A210494. 2
1, 35, 119, 527, 775, 819, 923, 2159, 2759, 3335, 5543, 6815, 6887, 12319, 13175, 13919, 21449, 23939, 24779, 37883, 47959, 64235, 83435, 111887, 124775, 127535, 128375, 128615, 167195, 189143, 206735, 221135, 240239, 254939, 278963, 343655, 351995, 357599, 373319 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..270 (terms 1..95 from Vincenzo Librandi)

Umberto Cerruti, Numeri Armonici e Numeri Perfetti, Blog matematico (in Italian), 2013. The sequence is on page 13.

MATHEMATICA

B[n_] := (n DivisorSigma[0, n] + DivisorSigma[2, n])/(2 DivisorSigma[1, n]); Select[Range[5 10^5], IntegerQ[B[#]] && ! PrimeQ[#] &]

PROG

(Magma) IsInteger := func<i | i eq Floor(i)>; [n: n in [1..5*10^5] | IsInteger((n*NumberOfDivisors(n)+DivisorSigma(2, n))/(2*SumOfDivisors(n))) and not IsPrime(n)];

CROSSREFS

Cf. A210494.

Sequence in context: A262455 A132144 A337233 * A284876 A216268 A098218

Adjacent sequences: A230211 A230212 A230213 * A230215 A230216 A230217

KEYWORD

nonn

AUTHOR

Bruno Berselli, Oct 11 2013

STATUS

approved

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Last modified December 4 02:16 EST 2022. Contains 358544 sequences. (Running on oeis4.)