A283919 The smallest square referenced in A013929 (Numbers that are not squarefree).

4, 4, 9, 4, 4, 9, 4, 4, 25, 9, 4, 4, 4, 4, 4, 9, 4, 49, 25, 4, 9, 4, 4, 9, 4, 4, 4, 25, 4, 4, 9, 4, 4, 9, 4, 4, 49, 9, 4, 4, 4, 4, 4, 9, 4, 121, 4, 25, 9, 4, 4, 9, 4, 4, 4, 49, 4, 25, 4, 9, 4, 4, 9, 4, 4, 169, 9, 4, 25, 4, 4, 4, 4, 9, 4, 4, 9, 4, 4, 9, 4, 4

Offset: 1

Author

Robert Price, Mar 17 2017

Keywords

• nonn

Examples

			A013929(4) = 12, 12 = 2*2*3, so 12 is not squarefree, the square being 2*2 = 4.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Robert Price)

Crossrefs

Cf. A013929, A046027.

Programs

Mathematica

s[n_] := If[(pos = Position[(f = FactorInteger[n])[[;; , 2]], ?(# >= 2 &)]) == {}, 1, f[[pos[[1, 1]], 1]]]; Select[Array[s, 250], # > 1 &]^2 (* _Amiram Eldar, Nov 14 2020 *)

PARI

f(n) = fordiv(n, d, if ((d>1) && issquare(d), return (d))); return (1);
apply(f, select(x->!issquarefree(x), [1..200])) \\ Michel Marcus, Nov 14 2020