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A053738 If n is in sequence then 2n and 2n+1 are not (and 1 is in the sequence); numbers with an odd number of digits in binary. 2
1, 4, 5, 6, 7, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Runs of successive numbers have lengths which are powers of 4.

Apparently, for any m>=1, 2^m is the largest power of 2 dividing sum(k=1,n,binomial(2k,k)^m) if and only if n is in the sequence. - Benoit Cloitre, Apr 27 2003

Numbers that begin with a 1 in base 4. - Michel Marcus, Dec 05 2013

LINKS

Table of n, a(n) for n=1..67.

MATHEMATICA

Select[Range[110], OddQ[IntegerLength[#, 2]]&] (* Harvey P. Dale, Sep 29 2012 *)

PROG

(PARI) isok(n, b=4) = digits(n, b)[1] == 1; \\ Michel Marcus, Dec 05 2013

CROSSREFS

Cf. A029837, A079112.

Sequence in context: A047566 A037355 A046300 * A154787 A233035 A107759

Adjacent sequences:  A053735 A053736 A053737 * A053739 A053740 A053741

KEYWORD

base,easy,nonn

AUTHOR

Henry Bottomley, Apr 06 2000

STATUS

approved

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Last modified December 21 12:47 EST 2014. Contains 252321 sequences.