This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A359644 #19 Jun 27 2025 17:28:32 %S A359644 0,0,0,24,910,18387,286758,3884936,48396263,571221133,6499261245, %T A359644 72047682376,783561421371,8399470576016,89038389261794, %U A359644 935562667202846,9761003371437806,101253973351371824,1045354835981786609 %N A359644 Number of numbers <= 10^n that are products of 5 distinct primes. %e A359644 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} %o A359644 (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 %Y A359644 Cf. A006880, A036351, A046387, A215218, A359642. %K A359644 nonn,more %O A359644 1,4 %A A359644 _Peter Dolland_, Jan 09 2023 %E A359644 a(14) from _Daniel Suteu_, Jan 10 2023 %E A359644 a(15)-a(19) from _Henri Lifchitz_, Feb 01 2025