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A063918
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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.
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1
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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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.
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LINKS
| Harry J. Smith, Table of n, a(n) for n=1,...,1000
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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) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Sep 02 2009]
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CROSSREFS
| A055396, A020639.
Sequence in context: A085341 A160812 A176866 * A163169 A097974 A139036
Adjacent sequences: A063915 A063916 A063917 * A063919 A063920 A063921
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KEYWORD
| nonn
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AUTHOR
| Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Sep 04 2001
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