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 A296243 Numbers k such that the multiplicative order of 2 modulo k is even. 4
 3, 5, 9, 11, 13, 15, 17, 19, 21, 25, 27, 29, 33, 35, 37, 39, 41, 43, 45, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 75, 77, 81, 83, 85, 87, 91, 93, 95, 97, 99, 101, 105, 107, 109, 111, 113, 115, 117, 119, 121, 123, 125, 129, 131, 133, 135, 137, 139, 141, 143, 145, 147, 149, 153 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Odd numbers k such that A007733(k) = A002326((k-1)/2) is even. LINKS Amiram Eldar, Table of n, a(n) for n = 1..10000 MATHEMATICA A036259 = Select[Range[1, 199, 2], OddQ[MultiplicativeOrder[2, #]] &]; Range[1, A036259[[-1]], 2] ~Complement~ A036259 (* Jean-François Alcover, Dec 20 2017 *) Select[Range[1, 153, 2], EvenQ[MultiplicativeOrder[2, #]] &] (* Amiram Eldar, Jul 30 2020 *) PROG (PARI) { is_A296243(n) = (n%2) && !(znorder(Mod(2, n))%2); } CROSSREFS Set difference of A005408 and A036259. Contains A296244 as a subsequence. The prime terms are given by A014662. Cf. A002326, A007733. Sequence in context: A304251 A309135 A088607 * A162699 A325129 A173263 Adjacent sequences:  A296240 A296241 A296242 * A296244 A296245 A296246 KEYWORD nonn AUTHOR Max Alekseyev, Dec 09 2017 STATUS approved

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Last modified April 20 09:21 EDT 2021. Contains 343125 sequences. (Running on oeis4.)