OFFSET
1,1
COMMENTS
The smallest number with six distinct prime divisors is the product of first six primes, 2*3*5*7*11 = 30030. The smallest number with seven distinct prime divisors is product of first seven primes, 2*3*5*7*11*13 = 390390.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
{n : A001221(n) = 6} . - R. J. Mathar, Jul 07 2012
EXAMPLE
60060 is in the sequence because 60060 = 2^2*3*5*7*11*13 with six distinct prime divisors 2, 3, 5, 7, 11, 13; 87780 is in the sequence because 87780 = 2^2*3*5*7*11*19 with six distinct prime divisors 2, 3, 5, 7, 11, 19.
MATHEMATICA
Select[Range[0, 5*8! ], Length[FactorInteger[ # ]]==6&] (* Vladimir Joseph Stephan Orlovsky, Apr 22 2010 *)
PROG
(PARI) is(n)=omega(n)==6 \\ Charles R Greathouse IV, Jun 19 2016
(PARI) A246655(lim)=my(v=List(primes([2, lim\=1]))); for(e=2, logint(lim, 2), forprime(p=2, sqrtnint(lim, e), listput(v, p^e))); Set(v)
list(lim, pr=6)=if(pr==1, return(A246655(lim))); my(v=List(), pr1=pr-1, mx=prod(i=1, pr1, prime(i))); forprime(p=prime(pr), lim\mx, my(u=list(lim\p, pr1)); for(i=1, #u, listput(v, p*u[i]))); Set(v) \\ Charles R Greathouse IV, Feb 03 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Zak Seidov, Oct 04 2002
STATUS
approved