A121993 Numbers n that yield a smaller number a(n) under the "Look and Say" function A045918.

33, 44, 55, 66, 77, 88, 99, 111, 222, 333, 444, 555, 666, 777, 888, 999, 1111, 1222, 1333, 1444, 1555, 1666, 1777, 1888, 1999, 2000, 2111, 2222, 2233, 2244, 2255, 2266, 2277, 2288, 2299, 2333, 2444, 2555, 2666, 2777, 2888, 2999, 3000, 3111, 3222, 3300, 3311

Offset

1,1

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Eric Weisstein's World of Mathematics, Look and Say Sequence.

Example

a(26)=2000 because under the Look and Say operator, 2000 is described as one two three zeros or: 1230, which is smaller than 2000.

Prog

(Haskell)
a121993 n = a121993_list !! (n-1)
a121993_list = filter (\x -> a045918 x < x) [0..]
-- Reinhard Zumkeller, Jan 25 2014
(Python)
from itertools import groupby
def ok(n): return n > int(''.join(str(len(list(g)))+k for k, g in groupby(str(n))))
print([k for k in range(3312) if ok(k)]) # Michael S. Branicky, May 26 2023

Crossrefs

Cf. A045918, A005150, A005341, A023989, A079475.

Sequence in context: A046041 A140151 A196579 * A225565 A050875 A060876

Adjacent sequences: A121990 A121991 A121992 * A121994 A121995 A121996

Keyword

easy,nonn,base

Author

Sergio Pimentel, Sep 11 2006

Status

approved