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A111565
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Largest prime factor of prime power > 1 that divides the n-th composite number; or a(n) = 0 iff n-th composite number is equal to the product of distinct primes.
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1
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2, 0, 2, 3, 0, 2, 0, 0, 2, 3, 2, 0, 0, 2, 5, 0, 3, 2, 0, 2, 0, 0, 0, 3, 0, 0, 2, 0, 2, 3, 0, 2, 7, 5, 0, 2, 3, 0, 2, 0, 0, 2, 0, 3, 2, 0, 0, 2, 0, 0, 3, 0, 5, 2, 0, 0, 2, 3, 0, 2, 0, 0, 0, 2, 3, 0, 2, 0, 0, 0, 2, 7, 3, 5, 0, 2, 0, 0, 3, 0, 0, 2, 0, 0, 2, 3, 0, 0, 2, 11, 0, 0, 2, 5, 3, 2, 0, 0, 2, 0, 0, 3
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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EXAMPLE
| a(6) = 2 because C(6) = 12 = 3*2^2 and the largest prime factor of power 2^2 is 2.
a(28) = 0 because C(28) = 42 = 2*3*7 is the product of distinct primes
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PROG
| (PARI) A002808(n)={for(k=0, primepi(n), isprime(n++)&k--); n} A111565(n)={local(f, r, i); f=factor(A002808(n)); r=0; i=matsize(f)[1]; while((r==0)&&(i>0), if(f[i, 2]>1, r=f[i, 1], i--)); r}
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CROSSREFS
| Cf. A002808 (composite numbers)
Sequence in context: A132814 A058623 A204329 * A141099 A127710 A137510
Adjacent sequences: A111562 A111563 A111564 * A111566 A111567 A111568
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KEYWORD
| nonn
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AUTHOR
| Giovanni Teofilatto (g.teofilatto(AT)tiscalinet.it), Nov 17 2005
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EXTENSIONS
| a(28) changed by Michael B. Porter (michael_b_porter(AT)yahoo.com), Feb 02 2010
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