A009293 If a, b in sequence, so is a*b+1.

2, 5, 11, 23, 26, 47, 53, 56, 95, 107, 113, 116, 122, 131, 191, 215, 227, 233, 236, 245, 254, 263, 266, 281, 287, 383, 431, 455, 467, 473, 476, 491, 509, 518, 527, 530, 533, 536, 563, 566, 575, 581, 584, 599, 611, 617, 656, 677, 767, 863, 911, 935, 947, 953, 956, 983

Offset

1,1

Links

Alois P. Heinz, Table of n, a(n) for n = 1..20000 (first 1000 terms from Reinhard Zumkeller)

Mathematica

f[l_] := Block[{k = l}, Select[ Union[ Flatten[ AppendTo[k, Table[ k[[i]]*k[[j]] + 1, {i, 1, Length[k]}, {j, 1, i}]]]], # < 1000 &]]; NestList[f, {2}, 7][[ -1]] (* Robert G. Wilson v, May 23 2004 *)

Prog

(Haskell)
import Data.Set (singleton, deleteFindMin, insert)
a009293 n = a009293_list !! (n-1)
a009293_list = f [2] (singleton 2) where
   f xs s = m : f xs' (foldl (flip insert) s' (map ((+ 1) . (* m)) xs'))
     where xs' = m : xs
           (m, s') = deleteFindMin s
-- Reinhard Zumkeller, Aug 15 2011

Crossrefs

Cf. A009388, A009299, A192476.

Sequence in context: A365243 A091617 A205880 * A180337 A257130 A038924

Adjacent sequences: A009290 A009291 A009292 * A009294 A009295 A009296

Keyword

nonn

Author

David W. Wilson

Status

approved