A156031 Alternate A022941 and A143344.

1, 2, 3, 5, 4, 9, 6, 15, 7, 22, 8, 30, 10, 40, 11, 51, 12, 63, 13, 76, 14, 90, 16, 106, 17, 123, 18, 141, 19, 160, 20, 180, 21, 201, 23, 224, 24, 248, 25, 273, 26, 299, 27, 326, 28, 354, 29, 383, 31, 414, 32, 446, 33, 479, 34, 513, 35, 548, 36, 584, 37, 621, 38, 659, 39, 698

Offset: 1

Author

N. J. A. Sloane, Nov 01 2009, based on a posting by Eric Angelini to the Sequence Fans Mailing List

Keywords

• nonn

Comments

Eric Angelini's definition was: start with 1,2,3; then alternately adjoin either the sum of the last two terms or the smallest number not yet in the sequence.

Links

• M. F. Hasler, Table of n, a(n) for n = 1..2001

Crossrefs

Cf. A022941, A143344, A167151, A005228, A030124.

Programs

Haskell

import Data.List (transpose)
a156031 n = a156031_list !! n
a156031_list = tail $ concat (transpose [a022941_list, a143344_list])
-- Reinhard Zumkeller, May 17 2013

PARI

f="b156031.txt"; used=[]; write(f,c=1," ",b=1);a=1; for(i=1,1e3, used=setunion(used,Set(a+=b)); while(setsearch(used,b++), used=setminus(used,Set(b))); write(f,c++," "a"\n",c++," "b)) \\ M. F. Hasler, Nov 01 2009