A249147 a(n) = 0 if A249148(n) = 1, otherwise the index of the least prime dividing A249148(n): a(n) = A055396(A249148(n)).

0, 1, 0, 2, 0, 1, 2, 1, 1, 1, 4, 0, 3, 0, 1, 1, 5, 0, 4, 1, 1, 1, 2, 1, 1, 1, 1, 9, 0, 1, 1, 2, 1, 1, 1, 11, 0, 2, 6, 1, 1, 12, 0, 1, 1, 2, 1, 1, 14, 0, 5, 2, 2, 1, 15, 0, 1, 4, 4, 1, 1, 1, 3, 2, 1, 1, 17, 0, 6, 3, 1, 1, 1, 2, 3, 1, 1, 1, 20, 0, 1, 1, 2, 1, 4, 2, 10, 0, 2, 1, 1, 22, 0, 1, 23, 0, 7

Offset: 1

Author

Antti Karttunen, Oct 24 2014

Keywords

• nonn

Links

• Antti Karttunen, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A049084, A055396, A249148.

Programs

PARI

A049084(n) = if(isprime(n), primepi(n), 0); \\ This function from Charles R Greathouse IV
A249147_write_bfile(up_to_n) = { my(pfcounts, n, a_n, x_n, f, k); pfcounts = vector(up_to_n); x_n = 1; for(n = 0, up_to_n, if((1 == x_n), pfcounts[1]++; x_n = pfcounts[1]; a_n = 0, f=factor(x_n); for(i=1,#f~,k = A049084(f[i,1])+1; pfcounts[k] += f[i,2]); a_n = A049084(f[1,1]); x_n = pfcounts[a_n+1]); if(n>0,write("b249147.txt", n, " ", a_n))); };
A249147_write_bfile(10000);

Scheme

(define (A249147 n) (A055396 (A249148 n)))

Formula

a(n) = A055396(A249148(n)).