A088377 a(n) = (smallest prime factor of n)^2; a(1) = 1.

1, 4, 9, 4, 25, 4, 49, 4, 9, 4, 121, 4, 169, 4, 9, 4, 289, 4, 361, 4, 9, 4, 529, 4, 25, 4, 9, 4, 841, 4, 961, 4, 9, 4, 25, 4, 1369, 4, 9, 4, 1681, 4, 1849, 4, 9, 4, 2209, 4, 49, 4, 9, 4, 2809, 4, 25, 4, 9, 4, 3481, 4, 3721, 4, 9, 4, 25, 4, 4489, 4, 9, 4, 5041, 4, 5329, 4, 9, 4

Offset: 1

Author

Reinhard Zumkeller, Sep 28 2003

Keywords

• nonn
• easy

Links

• Eric Weisstein's World of Mathematics, Least Prime Factor.
• Eric Weisstein's World of Mathematics, Square Number.

Crossrefs

Cf. A000290, A068319, A088378, A088379, A247180.

Programs

Mathematica

a[n_] := FactorInteger[n][[1, 1]]^2; Array[a, 100] (* Amiram Eldar, May 16 2025 *)

PARI

a(n) = if(n == 1, 1, factor(n)[1,1]^2); \\ Amiram Eldar, May 16 2025

Formula

a(n) = A000290(A020639(n)).

a(n) = sqrt(A088379(n)). - Amiram Eldar, May 16 2025