1,1

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 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

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

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

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]

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

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 *)

(Haskell) cf. Josh Triplett's program for A005051.

import Data.List (group)

a001140 n = a001140_list !! (n-1)

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

Cf. A001155, A005150, A006751, A006715, A001141, A001143, A001145, A001151, A001154.

Sequence in context: A292708 A367534 A112514 * A177363 A138488 A022508

Adjacent sequences: A001137 A001138 A001139 * A001141 A001142 A001143

nonn,base,easy,nice,changed

approved