A359644 Number of numbers <= 10^n that are products of 5 distinct primes.
0, 0, 0, 24, 910, 18387, 286758, 3884936, 48396263, 571221133, 6499261245, 72047682376, 783561421371, 8399470576016, 89038389261794, 935562667202846, 9761003371437806, 101253973351371824, 1045354835981786609
Offset: 1
Examples
a(4) = 24 = #{2310, 2730, 3570, 3990, 4290, 4830, 5610, 6006, 6090, 6270, 6510, 6630, 7410, 7590, 7770, 7854, 8610, 8778, 8970, 9030, 9282, 9570, 9690, 9870}
Programs
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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, 5); \\ Daniel Suteu, Jan 10 2023
Extensions
a(14) from Daniel Suteu, Jan 10 2023
a(15)-a(19) from Henri Lifchitz, Feb 01 2025