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 A190641 Numbers having exactly one non-unitary prime factor. 14
 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 Vaclav Kotesovec, Graph - the asymptotic ratio Carl Pomerance, Andrzej Schinzel, Multiplicative Properties of Sets of Residues, Moscow Journal of Combinatorics and Number Theory. 2011. Vol. 1. Iss. 1. pp. 52-66. See p. 61. FORMULA a(n) ~ k*n, where k = Pi^2/(6*A154945) = 2.9816096.... - 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 (PARI) isok(n) = my(f=factor(n)); #select(x->(x>1), f[, 2]) == 1; \\ Michel Marcus, Jul 30 2017 CROSSREFS Subsequence of A013929 and of A327877. Sequence in context: A289553 A013929 A162966 * A327877 A034043 A278517 Adjacent sequences:  A190638 A190639 A190640 * A190642 A190643 A190644 KEYWORD nonn AUTHOR Reinhard Zumkeller, Dec 29 2012 STATUS approved

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Last modified November 26 21:20 EST 2020. Contains 338641 sequences. (Running on oeis4.)