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A110502 Numbers n such that n in binary representation has a block of exactly a nontrivial square number of zeros. 2
16, 33, 48, 66, 67, 80, 97, 112, 132, 133, 134, 135, 144, 161, 176, 194, 195, 208, 225, 240, 264, 265, 266, 267, 268, 269, 270, 271, 272, 289, 304, 322, 323, 336, 353, 368, 388, 389, 390, 391, 400, 417, 432, 450, 451, 464, 481, 496, 512, 528, 529, 530, 531 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(n) is the index of zeros in the complement of the square analog of the Baum-Sweet sequence, which is b(n) = 1 if the binary representation of n contains no block of consecutive zeros of exactly a nontrivial square number length; otherwise b(n) = 0.

REFERENCES

J.-P. Allouche and J. Shallit, Automatic Sequences, Cambridge Univ. Press, 2003, p. 157.

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

J.-P. Allouche, Finite Automata and Arithmetic, Séminaire Lotharingien de Combinatoire, B30c (1993), 23 pp.

FORMULA

a(n) is in this sequence iff n (base 2) has a block (not a sub-block) of k^2 = A000290(k) consecutive zeros for k>1.

EXAMPLE

a(1) = 16 because 16 (base 2) = 10000, which has a block of 4 = 2^2 zeros.

a(2) = 33 because 33 (base 2) = 100001, which has a block of 4 zeros.

a(3) = 48 because 48 (base 2) = 110000, which has a block of 4 zeros.

a(49) = 512 because 512 (base 2) = 1000000000, with a block of 9 = 3^2 zeros.

Similarly, there are blocks of exactly 9 zeros in 1025, 1536, 2050, 2051, 3073, 3584, 7149, 8196, 8197, 8198, 8199.

65536, 131073, 196608, 262146 and 262147 are in this sequence because (base 2) they each have a block of 16 = 4^2 zeros.

33554432 has a block of 25 = 5^2 zeros.

MAPLE

filter:= proc(n) local L, nL, A, B;

  L:= convert(n, base, 2);

  nL:= nops(L);

  A:= select(t -> L[t]=0 and (t=1 or L[t-1]=1), [$1..nL]);

  B:= select(t -> L[t]=1 and L[t-1]=0, [$2..nL]);

  ormap(t -> t>3 and issqr(t), B-A)

end proc:select(filter, [$1..1000]); # Robert Israel, Sep 01 2021

MATHEMATICA

Select[Range[531], Or @@ (First[ # ] == 0 && Length[ # ] > 1 && IntegerQ[Length[ # ]^(1/2)] &) /@ Split[IntegerDigits[ #, 2]] &] (* Ray Chandler, Sep 12 2005 *)

PROG

(Python)

from math import isqrt

from itertools import groupby

def is_nt_sqr(n): # is nontrivial square

    return n > 1 and isqrt(n)**2 == n

def ok(n):

    b = bin(n)[2:]

    return any(k == '0' and is_nt_sqr(len(list(g))) for k, g in groupby(b))

print(list(filter(ok, range(532)))) # Michael S. Branicky, Sep 01 2021

CROSSREFS

Cf. A000290, A037011, A086747, A110471, A110472, A110474.

Sequence in context: A181452 A151981 A110472 * A095784 A041502 A041500

Adjacent sequences:  A110499 A110500 A110501 * A110503 A110504 A110505

KEYWORD

base,easy,nonn

AUTHOR

Jonathan Vos Post, Sep 11 2005

EXTENSIONS

Corrected and extended by Ray Chandler, Sep 12 2005

STATUS

approved

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Last modified May 27 16:48 EDT 2022. Contains 354110 sequences. (Running on oeis4.)