A071540 Number of k's less than or equal to 10^n such that there are no middle divisors of k (A071090).

4, 57, 664, 7068, 73130, 747244, 7590269

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: A353001 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