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A363469
Multiplicative order of 2 modulo 2*prime(n)+1.
0
4, 3, 10, 4, 11, 18, 12, 12, 23, 58, 6, 20, 82, 28, 36, 106, 24, 20, 36, 60, 42, 52, 83, 178, 12, 84, 66, 28, 18, 226, 8, 131, 20, 30, 132, 100, 12, 36, 132, 346, 179, 110, 191, 42, 156, 18, 138, 148, 12, 72, 466, 239, 66, 251, 204, 40, 210, 180, 36, 562, 54, 586
OFFSET
1,1
COMMENTS
In other words, least k > 0 such that 2*prime(n)+1 divides 2^k-1.
Iff 2*prime(n)+1 is prime then a(n) = prime(n) or 2*prime(n).
EXAMPLE
a(6) = 18 because 18 is the least integer such that 2^18 == 1 (mod 2*13+1) where 13 is prime(6).
MATHEMATICA
Table[MultiplicativeOrder[2, 2*Prime[n] + 1], {n, 1, 100}] (* Amiram Eldar, Jun 03 2023 *)
PROG
(PARI) a(n) = znorder(Mod(2, 2*prime(n)+1)); \\ Michel Marcus, Jun 04 2023
CROSSREFS
Cf. A002326.
Sequence in context: A107381 A242531 A275160 * A369710 A147756 A213768
KEYWORD
nonn
AUTHOR
Alain Rocchelli, Jun 03 2023
STATUS
approved