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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. 2
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

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