A181761 Start with 18; write down the sum of its digits; add last two terms; repeat.

18, 9, 27, 9, 36, 9, 45, 9, 54, 9, 63, 9, 72, 9, 81, 9, 90, 9, 99, 18, 117, 9, 126, 9, 135, 9, 144, 9, 153, 9, 162, 9, 171, 9, 180, 9, 189, 18, 207, 9, 216, 9, 225, 9, 234, 9, 243, 9, 252, 9, 261, 9, 270, 9, 279, 18, 297, 18, 315, 9, 324, 9, 333, 9, 342, 9

Offset: 1

Author

Anton Joha, Nov 14 2010

Keywords

• nonn
• base

Examples

			a(1)=18; a(2)=1+8=9; a(3)=18+9=27, etc.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A129888.

Programs

Mathematica

NestList[{Total[#],Total[IntegerDigits[Total[#]]]}&,{18,9},40]// Flatten (* Harvey P. Dale, Nov 10 2016 *)

Formula

a(2n+1) = A016096(n+2). - Michel Marcus, Oct 31 2014