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A038109 Divisible exactly by the square of a prime. 10

%I

%S 4,9,12,18,20,25,28,36,44,45,49,50,52,60,63,68,72,75,76,84,90,92,98,

%T 99,100,108,116,117,121,124,126,132,140,144,147,148,150,153,156,164,

%U 169,171,172,175,180,188,196,198,200,204,207,212,220,225,228,234,236,242

%N Divisible exactly by the square of a prime.

%C Numbers for which at least one prime factor exponent is exactly 2.

%C Sometimes called squarefull numbers, although that term is usually reserved for A001694. - _N. J. A. Sloane_, Jul 22 2012

%H R. J. Mathar, <a href="/A038109/b038109.txt">Table of n, a(n) for n = 1..1247</a>

%e 20=5*2*2 is divisible by 2^2.

%p isA038109 := proc(n)

%p local p;

%p for p in ifactors(n)[2] do

%p if op(2,p) = 2 then

%p return true;

%p end if;

%p end do:

%p false ;

%p end proc: # _R. J. Mathar_, Dec 08 2015

%t Select[Range[250],MemberQ[Transpose[FactorInteger[#]][[2]],2]&] (* _Harvey P. Dale_, Sep 24 2012 *)

%o (PARI) is(n)=#select(n->n==2, Set(factor(n)[,2])) \\ _Charles R Greathouse IV_, Sep 17 2015

%Y Cf. A001694, A013929, A284017, A284018.

%K nonn,easy

%O 1,1

%A _Felice Russo_

%E Corrected and extended by _Erich Friedman_

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Last modified May 31 16:29 EDT 2020. Contains 334748 sequences. (Running on oeis4.)