A175532 - OEIS

A175532

a(1) = 1; for n>1, a(n) = smallest number of the form 4k+1 and a(n) > a(n-1) such that the pairwise sums of elements are all semiprimes.

1, 9, 13, 25, 133, 193, 18673, 57313, 1032313, 4387273 (list; graph; refs; listen; history; text; internal format)

	OFFSET	`1,2`
	COMMENTS	`Or, for i<>j, (a(i)+a(j)/2 are primes.` `Starting with a(5)=133 on all terms === 13 mod 20.` `Is sequence finite?`
	LINKS	`Table of n, a(n) for n=1..10.`
	CROSSREFS	`Cf. A175533.` `Sequence in context: A242919 A097539 A107913 * A098074 A032361 A031196` `Adjacent sequences: A175529 A175530 A175531 * A175533 A175534 A175535`
	KEYWORD	`nonn`
	AUTHOR	`Zak Seidov, Jun 12 2010`
	STATUS	`approved`

Last modified January 27 02:34 EST 2023. Contains 359836 sequences. (Running on oeis4.)