

A009388


If a, b in sequence, so is a*b1.


4



2, 3, 5, 8, 9, 14, 15, 17, 23, 24, 26, 27, 29, 33, 39, 41, 44, 45, 47, 50, 51, 53, 57, 63, 65, 68, 69, 71, 74, 77, 80, 81, 84, 86, 87, 89, 93, 98, 99, 101, 105, 111, 113, 114, 116, 119, 122, 125, 129, 131, 134, 135, 137, 140, 141, 144, 147, 149, 152, 153, 158, 159, 161, 164
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OFFSET

1,1


COMMENTS

All terms are congruent to 0 or 2 mod 3. It follows that no three consecutive integers are in the sequence.  Franklin T. AdamsWatters, Aug 31 2016, conjectured by David W. Wilson.


LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..1000


MATHEMATICA

f[l_] := Block[{k = l}, Select[ Union[ Flatten[ AppendTo[k, Table[ k[[i]]*k[[j]]  1, {i, 1, Length[k]}, {j, 1, i}]]]], # < 170 &]]; NestList[f, {2}, 6][[ 1]] (* Robert G. Wilson v, May 23 2004 *)


PROG

(Haskell)
import Data.Set (singleton, deleteFindMin, insert)
a009388 n = a009388_list !! (n1)
a009388_list = f [2] (singleton 2) where
f xs s = m : f xs' (foldl (flip insert) s' (map (pred . (* m)) xs'))
where xs' = m : xs
(m, s') = deleteFindMin s
 Reinhard Zumkeller, Aug 15 2011


CROSSREFS

Cf. A009293. This is superset of A005659  1.
Cf. A009299, A192476.
Sequence in context: A058237 A251599 A270151 * A190803 A125871 A141399
Adjacent sequences: A009385 A009386 A009387 * A009389 A009390 A009391


KEYWORD

nonn


AUTHOR

David W. Wilson


STATUS

approved



