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A001155 Describe the previous term! (method A - initial term is 0). 16
0, 10, 1110, 3110, 132110, 1113122110, 311311222110, 13211321322110, 1113122113121113222110, 31131122211311123113322110, 132113213221133112132123222110 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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

a(n), A001140, A001141, A001143, A001145, A001151 and A001154 are all identical apart from the last digit of each term (the seed). This is because digits other than 1, 2 and 3 never arise elsewhere in the terms (other than at the end of each of them) of look-and-say sequences of this type (as is mentioned by Carmine Suriano in A006751). - Chayim Lowen, Jul 16 2015

REFERENCES

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, 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

S. R. Finch, Conway's Constant

EXAMPLE

E.g. the term after 3110 is obtained by saying "one 3, two 1's, one 0", which gives 132110.

MATHEMATICA

A001155[1] := 0; A001155[n_] := A001155[n] = FromDigits[Flatten[{Length[#], First[#]}&/@Split[IntegerDigits[A001155[n-1]]]]]; Map[A001155, Range[15]] (* Peter J. C. Moses, Mar 21 2013 *)

PROG

(PARI) A001155(n, a=0)={ while(n--, my(c=1); for(j=2, #a=Vec(Str(a)), if( a[j-1]==a[j], a[j-1]=""; c++, a[j-1]=Str(c, a[j-1]); c=1)); a[#a]=Str(c, a[#a]); a=concat(a)); a }  \\ M. F. Hasler, Jun 30 2011

CROSSREFS

Cf. A005150, A006751, A006715, A001140, A001141, A001143, A001145, A001151, A001154.

Cf. A036058.

Sequence in context: A204577 A210995 A036058 * A001391 A049064 A015026

Adjacent sequences:  A001152 A001153 A001154 * A001156 A001157 A001158

KEYWORD

nonn,base,easy,nice

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified August 31 06:53 EDT 2015. Contains 261232 sequences.