A065841 a(1) = 1; a(2) = 2; a(3) = 3; a(n) is concatenation of a(n-3), a(n-2) and a(n-1).

1, 2, 3, 123, 23123, 312323123, 12323123312323123, 2312331232312312323123312323123, 312323123123231233123231232312331232312312323123312323123

Offset

1,2

References

C. A. Pickover, "Wonders of Numbers", Oxford University Press, 2001, chapter 122 '3 Weird Problems with 3 - Growth', pp. 272-274, 378.

Links

Harry J. Smith, Table of n, a(n) for n=1..13

C. A. Pickover, "Wonders of Numbers, Adventures in Mathematics, Mind and Meaning," Zentralblatt review

Mathematica

nxt[{a_, b_, c_}]:={b, c, FromDigits[Flatten[IntegerDigits/@{a, b, c}]]}; Transpose[ NestList[nxt, {1, 2, 3}, 10]][[1]] (* Harvey P. Dale, Nov 08 2013 *)

Prog

(PARI) a(n)={my(a3=[1], a2=[2], a1=[3]); for(n=4, n, my(a=concat(concat(a3, a2), a1)); a3=a2; a2=a1; a1=a); fromdigits(if(n<3, [a3, a2][n], a1))} \\ Harry J. Smith, Nov 01 2009

Crossrefs

Cf. A065842, A001590.

Sequence in context: A102697 A041813 A065842 * A051177 A371271 A334661

Adjacent sequences: A065838 A065839 A065840 * A065842 A065843 A065844

Keyword

nonn,base,easy

Author

Patrick De Geest, Nov 27 2001

Extensions

Offset changed from 0 to 1 by Harry J. Smith, Nov 01 2009

Edited by Charles R Greathouse IV, Apr 27 2010

Status

approved