

A001140


Describe the previous term! (method A  initial term is 4).


15



4, 14, 1114, 3114, 132114, 1113122114, 311311222114, 13211321322114, 1113122113121113222114, 31131122211311123113322114, 132113213221133112132123222114, 11131221131211132221232112111312111213322114, 31131122211311123113321112131221123113111231121123222114
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OFFSET

1,1


COMMENTS

Method A = 'frequency' followed by 'digit'indication.
A001155, 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 lookandsay 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. 452455.
I. Vardi, Computational Recreations in Mathematica. AddisonWesley, 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. 173188.
S. R. Finch, Conway's Constant [Broken link]
S. R. Finch, Conway's Constant [From the Wayback Machine]


EXAMPLE

The term after 3114 is obtained by saying "one 3, two 1's, one 4", which gives 132114.


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, 4 ][ [ n ] ]; Table[ FromDigits[ F[ n ] ], {n, 1, 11} ] (* Zerinvary Lajos, Mar 21 2007 *)


PROG

(Haskell) cf. Josh Triplett's program for A005051.
import Data.List (group)
a001140 n = a001140_list !! (n1)
a001140_list = 4 : map say a001140_list where
say = read . concatMap saygroup . group . show
where saygroup s = (show $ length s) ++ [head s]
 Reinhard Zumkeller, Dec 15 2012
(Perl)
# This outputs the first n elements of the sequence, where n is given on the command line.
$s = 4;
for (2..shift @ARGV) {
print "$s, ";
$s =~ s/(.)\1*/(length $&).$1/eg;
}
print "$s\n";
## Arne 'Timwi' Heizmann (timwi(AT)gmx.net), Mar 12 2008)


CROSSREFS

Cf. A001155, A005150, A006751, A006715, A001141, A001143, A001145, A001151, A001154.
Sequence in context: A226943 A292708 A112514 * A177363 A138488 A022508
Adjacent sequences: A001137 A001138 A001139 * A001141 A001142 A001143


KEYWORD

nonn,base,easy,nice


AUTHOR

N. J. A. Sloane


STATUS

approved



