A001155 Describe the previous term! (method A - initial term is 0).

0, 10, 1110, 3110, 132110, 1113122110, 311311222110, 13211321322110, 1113122113121113222110, 31131122211311123113322110, 132113213221133112132123222110, 11131221131211132221232112111312111213322110, 31131122211311123113321112131221123113111231121123222110

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

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

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
(Python)
from itertools import accumulate, groupby, repeat
def summarize(n, _): return int("".join(str(len(list(g)))+k for k, g in groupby(str(n))))
def aupton(terms): return list(accumulate(repeat(0, terms), summarize))
print(aupton(11)) # Michael S. Branicky, Jun 28 2022

Crossrefs

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

Cf. A036058.

Sequence in context: A210995 A325910 A036058 * A001391 A049064 A267246

Adjacent sequences: A001152 A001153 A001154 * A001156 A001157 A001158

Keyword

nonn,base,easy,nice

Author

N. J. A. Sloane

Status

approved