id:A131208 - OEIS Search Results

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

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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; listen)

	OFFSET	`1,2`
	COMMENT	`Largest of all prime factors of the numbers between semiprime(n) and semiprime(n+1). Semiprime analogue 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	`Cf. A001358, A052248, A070552.` `Sequence in context: A116212 A079068 A133021 this_sequence A119479 A130008 A101809` `Adjacent sequences: A131205 A131206 A131207 this_sequence A131209 A131210 A131211`
	KEYWORD	`easy,more,nonn`
	AUTHOR	`Jonathan Vos Post (jvospost2(AT)yahoo.com), Oct 24 2007`
	EXTENSIONS	`Corrected and extended by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jan 15 2008`

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Last modified August 19 23:53 EDT 2008. Contains 142930 sequences.

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