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A121993
Numbers n that yield a smaller number a(n) under the "Look and Say" function A045918.
2
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
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
KEYWORD
easy,nonn,base
AUTHOR
Sergio Pimentel, Sep 11 2006
STATUS
approved