A001154 Describe the previous term! (method A - initial term is 9).

9, 19, 1119, 3119, 132119, 1113122119, 311311222119, 13211321322119, 1113122113121113222119, 31131122211311123113322119, 132113213221133112132123222119

Offset

1,1

Comments

Method A = 'frequency' followed by 'digit'-indication.

a(n+1) - a(n) is divisible by 10^5 for n > 5. - Altug Alkan, Dec 04 2015

References

S. R. Finch, Mathematical Constants, Cambridge, 2003, pp. 452-455.

I. Vardi, Computational Recreations in Mathematica. Addison-Wesley, Redwood City, CA, 1991, p. 4.

Links

T. D. Noe, Table of n, a(n) for n=1..20

J. H. Conway, The weird and wonderful chemistry of audioactive decay, in T. M. Cover and Gopinath, eds., Open Problems in Communication and Computation, Springer, NY 1987, pp. 173-188.

S. R. Finch, Conway's Constant [Broken link]

S. R. Finch, Conway's Constant [From the Wayback Machine]

Example

E.g. the term after 3119 is obtained by saying "one 3, two 1's, one 9", which gives 132119.

Mathematica

RunLengthEncode[x_List] := (Through[{First, Length}[ #1]] &) /@ Split[x]; LookAndSay[n_, d_: 1] := NestList[Flatten[Reverse /@ RunLengthEncode[ # ]] &, {d}, n - 1]; F[n_] := LookAndSay[n, 9][[n]]; Table[FromDigits[F[n]], {n, 1, 11}] (* Zerinvary Lajos, Jul 08 2009 *)

Crossrefs

Cf. A001155, A005150, A006751, A006715, A001140, A001141, A001143, A001145, A001151.

Sequence in context: A041160 A248305 A089565 * A177368 A138493 A022513

Adjacent sequences: A001151 A001152 A001153 * A001155 A001156 A001157

Keyword

nonn,base,easy,nice

Author

N. J. A. Sloane

Status

approved