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A131208
Greatest prime divisor of all composite numbers between n-th semiprime and next semiprime, or 1 if there are no such composite numbers.
0
1, 2, 1, 3, 1, 5, 1, 3, 1, 7, 1, 1, 3, 1, 11, 3, 5, 13, 7, 1, 5, 7, 17, 7, 19, 13, 7, 1, 1, 11, 23, 1, 1, 17, 11, 19, 29, 1, 5, 1, 1, 31, 13, 1, 23, 1, 1, 3, 1, 37, 13, 1, 5, 41, 7, 43, 1, 13, 23, 31, 47, 13, 1, 1, 17, 1, 23, 53, 1, 1, 3, 1, 1, 11, 37, 29, 59, 61, 31, 7
OFFSET
1,2
COMMENTS
Largest of all prime factors of the numbers between semiprime(n) and semiprime(n+1). Semiprime analog of A052248. a(A070552(n)) = 1. This sequence defines a mapping of semiprimes to primes.
FORMULA
a(n) = MAX{(A001358(n) < k < A001358(n+1), A006530(k))}.
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jonathan Vos Post, Oct 24 2007
EXTENSIONS
Corrected and extended by R. J. Mathar, Jan 15 2008
STATUS
approved