A131208 Greatest prime divisor of all composite numbers between n-th semiprime and next semiprime, or 1 if there are no such composite numbers.

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.

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 * A353467 A168008 A178810

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