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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 (list; graph; refs; listen; history; text; internal format)
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.

LINKS

Table of n, a(n) for n=1..80.

FORMULA

a(n) = MAX{(A001358(n) < k < A001358(n+1), A006530(k))}.

CROSSREFS

Cf. A001358, A052248, A070552.

Sequence in context: A116212 A079068 A133021 * A168008 A178810 A319627

Adjacent sequences:  A131205 A131206 A131207 * A131209 A131210 A131211

KEYWORD

easy,nonn

AUTHOR

Jonathan Vos Post, Oct 24 2007

EXTENSIONS

Corrected and extended by R. J. Mathar, Jan 15 2008

STATUS

approved

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Last modified October 18 01:39 EDT 2021. Contains 348065 sequences. (Running on oeis4.)