A001145 Describe the previous term! (method A - initial term is 7).

7, 17, 1117, 3117, 132117, 1113122117, 311311222117, 13211321322117, 1113122113121113222117, 31131122211311123113322117, 132113213221133112132123222117

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• base
• easy
• nice

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

Examples

			E.g. the term after 3117 is obtained by saying "one 3, two 1's, one 7", which gives 132117.
		

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]

Crossrefs

Cf. A001155, A005150, A006751, A006715, A001140, A001141, A001143, A001151, A001154.

Programs

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, 7][[n]]; Table[FromDigits[F[n]], {n, 1, 11}] (* Zerinvary Lajos, Jul 08 2009 *)