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 A053169 A paradoxical sequence: a positive integer n is in this sequence if and only if n is not in sequence A_n in the database. 1

%I

%S 4,7,9,11,12,13,15,17,18,20,21,22,23,24,25,28,29,30,31,32,33,34,35,38,

%T 39,40,41,42,43,44,45,46,47,48,49,50,51,53,54,55,56,57,58,60,61,63,64,

%U 65,66,67,68,70,71,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100

%N A paradoxical sequence: a positive integer n is in this sequence if and only if n is not in sequence A_n in the database.

%C "Not in sequence A_n" means not in the full list of terms, not simply in the list of terms visible in the entry.

%C The paradox is of course: is 53169 in this sequence?

%C Is 53873 in this sequence? - _Tanya Khovanova_, Aug 09 2007

%D Smullyan, Raymond M, What is the name of this book? : The riddle of Dracula and other logical puzzles, Englewood Cliffs, NJ : Prentice-Hall, c1978, see puzzle 163.

%e Sequence A000001 contains 1, so 1 is not in the sequence; A000002 contains 2, so 2 is not in the sequence; ...

%Y Cf. A037181.

%Y Complement of A053873.

%K nonn,nice

%O 1,1

%A Miklos Szabo (mike(AT)ludens.elte.hu), _N. J. A. Sloane_, Tue Feb 29 2000

%E Thanks to Alexander Hulpke (ahulpke(AT)math.ohio-state.edu) for the information that 19 is in A000019.

%E Extended to n=100 by _N. J. A. Sloane_, May 26 2007

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