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A091011 Numbers having at least one divisor, d, such that for some x, d-x and d+x are also divisors. 7
6, 12, 15, 18, 24, 28, 30, 36, 40, 42, 45, 48, 54, 56, 60, 66, 72, 75, 78, 80, 84, 90, 91, 96, 102, 105, 108, 112, 114, 120, 126, 132, 135, 138, 140, 144, 150, 153, 156, 160, 162, 165, 168, 174, 180, 182, 186, 190, 192, 195, 196, 198, 200, 204, 210, 216, 220 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A091009(a(n)) > 0; complement of A091010.

Numbers k with at least one pair of divisors, (d1,d2), with d1 < d2, whose (integer) average divides k. - Wesley Ivan Hurt, Aug 23 2020

LINKS

Table of n, a(n) for n=1..57.

MATHEMATICA

Table[If[Sum[Sum[(1 - Ceiling[(i + k)/2] + Floor[(i + k)/2]) (1 - Ceiling[2 n/(i + k)] + Floor[2 n/(i + k)]) (1 - Ceiling[n/k] + Floor[n/k]) (1 - Ceiling[n/i] + Floor[n/i]), {i, k - 1}], {k, n}] > 0, n, {}], {n, 200}] // Flatten (* Wesley Ivan Hurt, Aug 23 2020 *)

CROSSREFS

Cf. A091009, A091010, A337331.

Sequence in context: A290965 A315615 A315616 * A324771 A104210 A066312

Adjacent sequences:  A091008 A091009 A091010 * A091012 A091013 A091014

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Dec 13 2003

STATUS

approved

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Last modified May 17 19:39 EDT 2021. Contains 343988 sequences. (Running on oeis4.)