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A102300 Number of distinct prime divisors of n where n and n+1 are composite or twin composite numbers. 0

%I

%S 1,1,2,2,2,2,2,1,2,1,1,2,2,2,2,2,2,2,2,1,2,2,2,2,2,2,2,2,1,2,2,2,2,2,

%T 2,2,2,1,3,2,2,2,3,2,2,2,2,2,2,2,2,3,3,2,3,2,2,2,2,2,3,1,2,2,2,1,1,2,

%U 3,2,2,2,3,2,2,2,2,2,2,2,2,2,3,2,2,2,2,2,2,3,3,1,3,2,3,2,2,2,3,2,2,2,3,2,2

%N Number of distinct prime divisors of n where n and n+1 are composite or twin composite numbers.

%e For n=8 n+1=9 a twin composite pair. 8=2^3 has 1 distinct divisor, 2.

%o (PARI) f2(n) = for(x=1,n,y=composite(x);if(!isprime(y+1),print1(omega(y)","))) composite(n) =\The n-th composite number. 1 is def as not prime nor composite. { local(c,x); c=1; x=1; while(c <= n, x++; if(!isprime(x),c++); ); return(x) }

%K easy,nonn

%O 1,3

%A _Cino Hilliard_, Feb 19 2005

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Last modified June 27 13:59 EDT 2022. Contains 354896 sequences. (Running on oeis4.)