A129888 -id:A129888 - cp's OEIS frontend

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

Anton Joha, Nov 14 2010

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

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

Cf. A129888.

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

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

A120310 See comments lines.

Original entry on oeis.org

98, 72, 77, 49, 54, 20, 10, 1, 11, 2, 13, 4, 17, 8, 25, 7, 1, 2, 2, 6, 3, 12, 4, 20, 5, 15, 20, 13, 18, 11, 0, 0, 4, 9, 8, 18, 12, 27

Offset: 1

Sydney Richardson (AmyNStiers(AT)aol.com), Aug 16 2006

Comment from Joshua Zucker, May 26 2007. This appears to be a concatenation of five puzzles:
98,72,77,49,54,20,25,10,15,5,10,0,5,5,10,0,5,5,10,0,... (start with 98, then write down the product of its digits, then add 5, repeat) - see A129887.
10,1,11,2,13,4,17,8,25,7,... (start with 10; write down the sum of its digits; add last two terms; repeat) - see A129888.
1,2,2,6,3,12,4,20,5,30,6,42,... (write down n, then n(n+1)) - see A129889.
15,20,13,18,11,16,9,14,... (interleave two arithmetic progressions of difference -2).
0,0,4,9,8,18,12,27,16,36,20,... (interleave two arithmetic progressions 0,4,8,12,... and 0,9,18,27,...)

cp's OEIS Frontend

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

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A120310 See comments lines.

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