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 A197861 Prime divisor of n which appears the fewest times previously in the sequence, with ties to the smaller prime. 1
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 LINKS EXAMPLE 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. PROG (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])]

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Last modified January 21 17:07 EST 2019. Contains 319350 sequences. (Running on oeis4.)