OFFSET
1,1
COMMENTS
n belongs to this sequence iff exactly one prime in its factorization into prime powers has exponent 2 and all the other primes in the factorization have exponent 1, for example 60 = 2^2 * 3 * 5.
Numbers n such that A046660(n) = 1. - Zak Seidov, Nov 14 2012
LINKS
Enrique Pérez Herrero, Table of n, a(n) for n = 1..5000
Eckford Cohen, Arithmetical notes. VIII. An asymptotic formula of Rényi, Proc. Amer. Math. Soc. 13 (1962), pp. 536-539.
FORMULA
MATHEMATICA
Select[Range[500], PrimeOmega[#] - PrimeNu[#] == 1 &] (* Harvey P. Dale, Sep 08 2011 *)
PROG
(PARI) for(n=1, 279, if(bigomega(n)-omega(n)==1, print1(n, ", ")))
(PARI) is(n)=factorback(factor(n)[, 2])==2 \\ Charles R Greathouse IV, Sep 18 2015
(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), t=k^2; 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
(Haskell)
a060687 n = a060687_list !! (n-1)
a060687_list = filter ((== 1) . a046660) [1..]
-- Reinhard Zumkeller, Nov 29 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Ahmed Fares (ahmedfares(AT)my-deja.com), Apr 19 2001
EXTENSIONS
Corrected and extended by Vladeta Jovovic, Jul 05 2001
STATUS
approved