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A249729 Numbers not fixed by A250249 and A250250. 5


%S 21,27,33,39,42,45,51,54,55,57,63,65,66,69,73,75,78,81,84,85,87,90,91,

%T 93,95,99,102,103,105,108,110,111,114,115,117,119,123,125,126,129,130,

%U 132,133,135,137,138,141,145,146,150,155,156,159,161,162,165,167,168,170,171,174,175,177,180,181,182,183,185,186,187,189,190,195,197,198,201

%N Numbers not fixed by A250249 and A250250.

%C Numbers for which A250249(n) <> n (equally: A250250(n) <> n).

%C If n is a member, then 2n is also a member. If any 2n is a member, then n is also a member. If n is a member, then the n-th prime, p_n (= A000040(n)) is also a member. If p_n is a member, then its index n is also a member. Thus the sequence is completely determined by its odd nonprime terms: 21, 27, 33, 39, 45, ..., and is obtained as a union of their multiples with powers of 2, and all prime recurrences that start with those values. For example, because 21 is present, then 2*21 = 42 is also present. Furthermore, 73 = p_21 is also present, as well as 367 = p_73 as well as 181 = p_42. See also comments at A250251 and A250249.

%o (Scheme, with _Antti Karttunen_'s IntSeq-library)

%o (define A249729 (MATCHING-POS 1 1 (lambda (n) (not (= n (A250249 n))))))

%Y Complement: A250251.

%Y Cf. A000040, A250249, A250250.

%K nonn

%O 1,1

%A _Antti Karttunen_, Nov 18 2014

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Last modified April 7 10:56 EDT 2020. Contains 333301 sequences. (Running on oeis4.)