A359642 Number of numbers <= 10^n that are products of 4 distinct primes.

0, 0, 16, 429, 7039, 92966, 1103888, 12364826, 133702610, 1413227318, 14709861824, 151469044739, 1547593008310, 15721130285808, 159006397271949, 1602820838558101, 16114386617828822, 161673560523193369, 1619352576852638084, 16197963371445222701

Offset

1,3

Links

Table of n, a(n) for n=1..20.

Example

a(3) = 16 = #{210, 330, 390, 462, 510, 546, 570, 690, 714, 770, 798, 858, 870, 910, 930, 966}

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, 4); \\ Daniel Suteu, Jan 11 2023

Crossrefs

Cf. A006880, A046386, A036351, A215218.

Sequence in context: A202546 A220286 A322713 * A275035 A275140 A274731

Adjacent sequences: A359639 A359640 A359641 * A359643 A359644 A359645

Keyword

nonn

Author

Peter Dolland, Jan 09 2023

Extensions

a(14)-a(15) from Daniel Suteu, Jan 11 2023

a(16)-a(20) from Henri Lifchitz, Jan 31 2025

Status

approved