A036116 - OEIS

A036116

Numbers n such that the number of distinct primes dividing n is a square.

1, 2, 3, 4, 5, 7, 8, 9, 11, 13, 16, 17, 19, 23, 25, 27, 29, 31, 32, 37, 41, 43, 47, 49, 53, 59, 61, 64, 67, 71, 73, 79, 81, 83, 89, 97, 101, 103, 107, 109, 113, 121, 125, 127, 128, 131, 137, 139, 149, 151, 157, 163, 167, 169, 173, 179, 181, 191, 193, 197, 199, 210, 211, 223, 227, 229, 233, 239, 241, 243, 251, 256, 257, 263, 269, 271, 277, 281

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OFFSET

1,2

LINKS

Enrique Pérez Herrero, Table of n, a(n) for n = 1..5000

EXAMPLE

8 = 2^3 is divisible by just one (distinct) prime, 2 and 1 is a square, so 8 is in the sequence.

MAPLE

readlib(issqr): with(numtheory): select(x->issqr(nops(factorset(x))), [ seq(n, n=1..300) ]);

MATHEMATICA

Select[Range[100], IntegerQ[PrimeNu[#]^(1/2)]&] (* Enrique Pérez Herrero, Jul 07 2012 *)

PROG