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A239137 The sequence S = a(1), a(2), ... is defined by a(1)=1, if d,e,f are consecutive digits then we do not have d <= e <= f, and S is always extended with the smallest integer not yet present in S. 1

%I #23 Dec 17 2021 02:16:38

%S 1,2,10,3,12,13,14,15,4,5,16,17,6,7,18,19,8,9,20,21,30,31,32,40,41,42,

%T 43,22,102,103,23,24,25,26,27,28,29,33,104,34,35,36,37,38,39,44,105,

%U 45,46,47,48,49,50,51,52,53,54,60,61,62,63,64,65,70,71,72,73

%N The sequence S = a(1), a(2), ... is defined by a(1)=1, if d,e,f are consecutive digits then we do not have d <= e <= f, and S is always extended with the smallest integer not yet present in S.

%C Computed by Lars Blomberg.

%C Numbers a(n) = 0, 1, 11 (mod 100) cannot be added to this sequence, otherwise the sequence would terminate with 1, 2, 10, 3, 11. - _Gleb Ivanov_, Dec 06 2021

%D Eric Angelini, Posting to Sequence Fans Mailing List, Sep 28 2013

%H Eric Angelini, <a href="http://www.cetteadressecomportecinquantesignes.com/LittleEqualGreat.htm">Less than <, Equal to =, Greater than ></a> (see sequence Sg)

%H Eric Angelini, <a href="/A239083/a239083.pdf">Less than <, Equal to =, Greater than ></a> [Cached copy, with permission of the author]

%o (Python)

%o is_ok = lambda s: not any(s[i-2] <= s[i-1] <= s[i] for i in range(2, len(s)))

%o terms, appears, digits = [1], {1}, '1'

%o for i in range(100):

%o t = 1

%o while not(

%o t not in appears

%o and is_ok(digits + str(t))

%o and t % 100 not in [0, 1, 11]

%o ): t += 1

%o terms.append(t); appears.add(t); digits = digits + str(t)

%o digits = digits[-2:]

%o print(terms) # _Gleb Ivanov_, Dec 06 2021

%Y The sequences in this family are given in A239083-A239086, A239136-A239139, A239087-A239090, A239215-A239218, A239235.

%K nonn,base

%O 1,2

%A _Michel Marcus_, Mar 11 2014

%E a(56) corrected by _Gleb Ivanov_, Dec 17 2021

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Last modified March 29 09:59 EDT 2024. Contains 371268 sequences. (Running on oeis4.)