A099441 - OEIS

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A099441

Numbers n such that A000295(n)=2^n-n-1 is a semiprime.

3, 5, 6, 8, 9, 12, 30, 32, 33, 46, 52, 62, 74, 76, 86, 98, 130, 134, 154, 228, 230, 242, 256, 166, 346, 352, 382, 412, 428, 474, 488 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,1`
	COMMENTS	`A candidate for the next term is a(32)=634. 2^634-635 is composite with 191 decimal digits and unknown factorization. - Hugo Pfoertner (hugo(AT)pfoertner.org), Aug 13 2007`
	LINKS	`Dario Alpern, Factorization using the Elliptic Curve Method.`
	EXAMPLE	`a(3)=6 because 2^6-6-1=57=3*19 is a semiprime.`
	CROSSREFS	`Cf. A000295 2^n-n-1 (column 2 of the Eulerian numbers), A099439 2^n-n-1 is prime, A099440 primes in A000295, A099442 semiprimes in A000295.` `Sequence in context: A047446 A058065 A164902 * A129359 A110801 A078339` `Adjacent sequences: A099438 A099439 A099440 * A099442 A099443 A099444`
	KEYWORD	`hard,nonn`
	AUTHOR	`Hugo Pfoertner (hugo(AT)pfoertner.org), Oct 18 2004`
	EXTENSIONS	`More terms from Hugo Pfoertner (hugo(AT)pfoertner.org), Aug 13 2007`

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Last modified February 15 14:37 EST 2012. Contains 205822 sequences.