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A283050 Integers that are divisible by the square of their least prime factor. 12
4, 8, 9, 12, 16, 20, 24, 25, 27, 28, 32, 36, 40, 44, 45, 48, 49, 52, 56, 60, 63, 64, 68, 72, 76, 80, 81, 84, 88, 92, 96, 99, 100, 104, 108, 112, 116, 117, 120, 121, 124, 125, 128, 132, 135, 136, 140, 144, 148, 152, 153, 156, 160, 164, 168, 169, 171, 172, 175, 176, 180 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Integers > 1 such that A126773(n) = 1.

Conjecture: 1 <= a(n+1) - a(n) <= 4. - R. J. Cano, Feb 27 2017

The conjecture is true since all multiples of 4 are in this sequence. - Charles R Greathouse IV, Feb 28 2017

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

FORMULA

a(n) ~ kn where 1/k = 1/2^2 + 1/2*1/3^2 + 1/2*2/3*1/5^2 + 1/2*2/3*4/5*1/7^2 + ... = A283071 so k = 3.02940306.... - Charles R Greathouse IV, Feb 27 2017

MAPLE

A283050 := proc(n)

option remember;

if n =1 then

4 ;

else

for a from procname(n-1)+1 do

if A126773(a)= 1 then

return a;

end if;

end do:

end if;

end proc:

seq(A283050(n), n=1..100) ; # R. J. Mathar, Mar 03 2017

MATHEMATICA

Select[Range[2, 180], Divisible[#, FactorInteger[#][[1, 1]]^2] &] (* Michael De Vlieger, Feb 27 2017 *)

PROG

(PARI) isok(n) = !(n % factor(n)[1, 1]^2);

CROSSREFS

Subsequence of A013929 (numbers that are not squarefree).

Cf. A126773, A283071.

Sequence in context: A034030 A057109 A069189 * A069168 A102211 A244032

Adjacent sequences: A283047 A283048 A283049 * A283051 A283052 A283053

KEYWORD

nonn

AUTHOR

Michel Marcus, Feb 27 2017

STATUS

approved

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Last modified February 4 14:20 EST 2023. Contains 360055 sequences. (Running on oeis4.)