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 A367231 Carmichael numbers k such that the multiplicative order of 2 modulo k is odd. 2
 15841, 52633, 5049001, 68154001, 104852881, 238244041, 382536001, 3215031751, 3863326897, 7211236033, 8214723001, 15462960481, 22008493921, 23000028481, 29392867201, 31708772257, 41217865921, 53125756201, 60518537641, 74190097801, 77874636001, 83828294551, 103387371361 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS These Carmichael numbers seem to be relatively rare: among the 4279356 Carmichael numbers below 2^64 only 3097 are terms of this sequence. LINKS Amiram Eldar, Table of n, a(n) for n = 1..10000 (calculated using data from Claude Goutier) Claude Goutier, Compressed text file carm10e22.gz containing all the Carmichael numbers up to 10^22. Index entries for sequences related to Carmichael numbers. MATHEMATICA Select[2*Range[3*10^6] + 1, Mod[#, CarmichaelLambda[#]] == 1 && CompositeQ[#] && OddQ[MultiplicativeOrder[2, #]] &] PROG (PARI) is(n) = n > 1 && n % 2 && !isprime(n) && n % lcm(znstar(n)[2]) == 1 && znorder(Mod(2, n)) % 2; CROSSREFS Intersection of A002997 and A036259. Subsequence of A367230. Cf. A002326, A163956. Sequence in context: A216180 A112450 A063847 * A265669 A356866 A184612 Adjacent sequences: A367228 A367229 A367230 * A367232 A367233 A367234 KEYWORD nonn AUTHOR Amiram Eldar, Nov 11 2023 STATUS approved

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Last modified June 19 18:58 EDT 2024. Contains 373507 sequences. (Running on oeis4.)