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A071540 Number of k's less than or equal to 10^n such that there are no middle divisors of k (A071090). 1
4, 57, 664, 7068, 73130, 747244, 7590269 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..7.

MATHEMATICA

f[n_] := Plus @@ Select[ Divisors[n], Sqrt[n/2] <= # < Sqrt[n*2] &]; s = 0; k = 0; Do[ While[k < 10^n, k++; If[ f[k] == 0, s++ ]]; Print[s], {n, 1, 7}]

CROSSREFS

Cf. A071541.

Sequence in context: A181437 A156873 A320977 * A298764 A299562 A299459

Adjacent sequences:  A071537 A071538 A071539 * A071541 A071542 A071543

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, May 31 2002

STATUS

approved

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Last modified June 5 18:48 EDT 2020. Contains 334854 sequences. (Running on oeis4.)