A121993 Numbers k that yield a smaller number a(k) 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

Author

Sergio Pimentel, Sep 11 2006

Keywords

• easy
• nonn
• base
• changed

Examples

			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.
		

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
• Eric Weisstein's World of Mathematics, Look and Say Sequence.

Crossrefs

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

Programs

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