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) digitsIn(x)= { local(d); if (x==0, return(1)); d=1 + log(x)\log(10); if (10^d == x, d++, if (10^(d-1) > x, d--)); return(d) } Concat(a, b)= { return(a*10^digitsIn(b) + b) } { for (n = 1, 13, if (n>3, a=Concat(Concat(a3, a2), a1); a3=a2; a2=a1; a1=a, if (n==1, a=a3=1, if (n==2, a=a2=2, a=a1=3))); write("b065841.txt", n, " ", a) ) } \\ 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