A082293 Numbers having exactly one square divisor > 1.

4, 8, 9, 12, 18, 20, 24, 25, 27, 28, 40, 44, 45, 49, 50, 52, 54, 56, 60, 63, 68, 75, 76, 84, 88, 90, 92, 98, 99, 104, 116, 117, 120, 121, 124, 125, 126, 132, 135, 136, 140, 147, 148, 150, 152, 153, 156, 164, 168, 169, 171, 172, 175, 184, 188, 189, 198, 204, 207, 212

Offset

1,1

Comments

Numbers of the form m*p^2, p prime and m squarefree (A005117). [Corrected by Peter Munn, Nov 17 2020]

The asymptotic density of this sequence is (6/Pi^2)*Sum_{n>=1} 1/prime(n)^2 = 0.274933... (A222056). - Amiram Eldar, Jul 07 2020

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Formula

A046951(a(n)) = 2.

Mathematica

Select[Range[2, 200], MemberQ[{2, 3}, (e = Sort[FactorInteger[#][[;; , 2]]])[[-1]]] && (Length[e] == 1 || e[[-2]] == 1) &] (* Amiram Eldar, Jul 07 2020 *)

Prog

(PARI) is(n)=my(f=vecsort(factor(n)[, 2], , 4)); #f && f[1]>1 && f[1]<4 && (#f==1 || f[2]==1) \\ Charles R Greathouse IV, Oct 16 2015

Crossrefs

Cf. A005117, A046951, A222056.

Complement of A048111 within A013929.

Subsequence of A252849.

Disjoint union of A048109 and A060687.

A285508 is a subsequence.

Sequence in context: A074661 A370076 A252849 * A048944 A211658 A235054

Adjacent sequences: A082290 A082291 A082292 * A082294 A082295 A082296

Keyword

nonn

Author

Reinhard Zumkeller, Apr 08 2003

Status

approved