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A359645
Number of numbers <= 10^n that are products of 6 distinct primes.
0
0, 0, 0, 0, 20, 1235, 32396, 605939, 9446284, 131733664, 1706815354, 21008871506, 249145286508, 2873325692759
OFFSET
1,5
EXAMPLE
a(5) = 20 = #{30030, 39270, 43890, 46410, 51870, 53130, 62790, 66990, 67830, 71610, 72930, 79170, 81510, 82110, 84630, 85470, 91770, 94710, 98670, 99330}.
PROG
(PARI) a(n) = my(N=10^n); (f(m, p, k, j=1)=my(s=sqrtnint(N\m, k), count=0); if(k==2, forprime(q=p, s, count += primepi(N\(m*q)) - j; j+=1); return(count)); forprime(q=p, s, count += f(m*q, q+1, k-1, j+1); j+=1); count); f(1, 2, 6); \\ Daniel Suteu, Jan 11 2023
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Peter Dolland, Jan 09 2023
EXTENSIONS
a(13)-a(14) from Daniel Suteu, Jan 11 2023
STATUS
approved