A197861 Prime divisor of n which appears the fewest times previously in the sequence, with ties to the smaller prime.

2, 3, 2, 5, 3, 7, 2, 3, 5, 11, 2, 13, 7, 5, 2, 17, 3, 19, 5, 7, 11, 23, 3, 5, 13, 3, 7, 29, 2, 31, 2, 11, 17, 7, 3, 37, 19, 13, 5, 41, 7, 43, 11, 5, 23, 47, 2, 7, 5, 17, 13, 53, 3, 11, 7, 19, 29, 59, 2, 61, 31, 3, 2, 13, 11, 67, 17, 23, 5, 71, 3, 73, 37, 5, 19

Offset: 2

Author

Franklin T. Adams-Watters, Oct 18 2011

Keywords

• nonn

Examples

			The only prime divisor of 4 is 2, so a(4) = 2.
The prime divisors of 6 are 2 and 3; in the sequence to that point (2,3,2,5), there are two 2's and 1 3, we take the less common one, so a(6) = 3.
The prime divisors of 12 are 2 and 3; these occur equally often in the sequence to that point, so we take the smaller one; a(12)=2.
		

Crossrefs

Cf. A197862, A006530.

Programs

PARI

al(n)={local(ns=vector(primepi(n)),r=vector(n-1),ps);
  for(k=1,n-1,
    ps=factor(k+1)[,1]~;
    r[k]=ps[1];
    for(j=2,#ps,if(ns[primepi(ps[j])]