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A283050
Integers that are divisible by the square of their least prime factor.
20
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
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).
Sequence in context: A069189 A375399 A371601 * A069168 A374037 A102211
KEYWORD
nonn
AUTHOR
Michel Marcus, Feb 27 2017
STATUS
approved