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A063918
a(1) = 1 and - applying the sieve of Eratosthenes - for n > 1: a(n) = if n is prime then 0 else the first prime p which marks n as composite.
2
1, 0, 0, 2, 0, 2, 0, 2, 3, 2, 0, 2, 0, 2, 3, 2, 0, 2, 0, 2, 3, 2, 0, 2, 5, 2, 3, 2, 0, 2, 0, 2, 3, 2, 5, 2, 0, 2, 3, 2, 0, 2, 0, 2, 3, 2, 0, 2, 7, 2, 3, 2, 0, 2, 5, 2, 3, 2, 0, 2, 0, 2, 3, 2, 5, 2, 0, 2, 3, 2, 0, 2, 0, 2, 3, 2, 7, 2, 0, 2, 3, 2, 0, 2, 5, 2, 3, 2, 0, 2, 7, 2, 3, 2, 5, 2, 0, 2, 3, 2, 0, 2, 0, 2, 3
OFFSET
1,4
COMMENTS
k > 1: a(k*2) = 2, as all even numbers > 2 are marked by 2; for all primes p: a(p^k) = p and a(i) < p for i < p^2.
LINKS
PROG
(PARI) { for (n=1, 1000, if (n==1, p=1, if (isprime(n), p=0, p=1; until (n%p == 0, p=nextprime(p + 1)))); write("b063918.txt", n, " ", p) ) } \\ Harry J. Smith, Sep 02 2009
CROSSREFS
Sequence in context: A176866 A294614 A347403 * A271419 A278922 A163169
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Sep 04 2001
STATUS
approved