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A111565 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. 1
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; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..102.

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

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}

CROSSREFS

Cf. A002808 (composite numbers)

Sequence in context: A058623 A209689 A204329 * A299761 A141099 A127710

Adjacent sequences: A111562 A111563 A111564 * A111566 A111567 A111568

KEYWORD

nonn

AUTHOR

Giovanni Teofilatto, Nov 17 2005

EXTENSIONS

a(28) changed by Michael B. Porter, Feb 02 2010

STATUS

approved

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Last modified February 3 01:24 EST 2023. Contains 360024 sequences. (Running on oeis4.)