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A190641 Numbers having exactly one non-unitary prime factor. 6
4, 8, 9, 12, 16, 18, 20, 24, 25, 27, 28, 32, 40, 44, 45, 48, 49, 50, 52, 54, 56, 60, 63, 64, 68, 75, 76, 80, 81, 84, 88, 90, 92, 96, 98, 99, 104, 112, 116, 117, 120, 121, 124, 125, 126, 128, 132, 135, 136, 140, 147, 148, 150, 152, 153, 156, 160, 162, 164 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A056170(a(n)) = 1.

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

FORMULA

a(n) ~ kn, where k = 1/A154945 = 1.8126013.... - Charles R Greathouse IV, Aug 02 2016

MATHEMATICA

Select[Range[164], Count[FactorInteger[#][[All, 2]], 1] == Length[FactorInteger[#]] - 1 &] (* Geoffrey Critzer, Feb 05 2015 *)

PROG

(Haskell)

a190641 n = a190641_list !! (n-1)

a190641_list = map (+ 1) $ elemIndices 1 a056170_list

(PARI) list(lim)=my(s=lim\4, v=List(), u=vectorsmall(s, i, 1), t, x); forprime(k=2, sqrtint(s), t=k^2; forstep(i=t, s, t, u[i]=0)); forprime(k=2, sqrtint(lim\1), for(e=2, logint(lim\1, k), t=k^e; for(i=1, #u, if(u[i] && gcd(k, i)==1, x=t*i; if(x>lim, break); listput(v, x))))); Set(v) \\ Charles R Greathouse IV, Aug 02 2016

CROSSREFS

Subsequence of A013929.

Sequence in context: A289553 A013929 A162966 * A034043 A278517 A053443

Adjacent sequences:  A190638 A190639 A190640 * A190642 A190643 A190644

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Dec 29 2012

STATUS

approved

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Last modified July 22 03:22 EDT 2017. Contains 289648 sequences.