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A375793
Numbers m such that 2^m == 2 (mod m-th triangular number).
2
1, 3, 5, 11, 13, 29, 37, 61, 73, 131, 157, 181, 193, 277, 313, 397, 421, 457, 541, 561, 613, 661, 673, 733, 757, 877, 997, 1093, 1153, 1201, 1213, 1237, 1289, 1321, 1381, 1453, 1621, 1657, 1753, 1873, 1905, 1933, 1993, 2017, 2137, 2341, 2473, 2557, 2593, 2797, 2857, 2917, 3061, 3217, 3253, 3313, 3389, 3457
OFFSET
1,2
COMMENTS
a(19) = 561 is the first composite term of the sequence.
LINKS
MAPLE
t:= n-> n*(n+1)/2:
q:= m-> is(2&^m-2 mod t(m)=0):
select(q, [$1..3457])[]; # Alois P. Heinz, Sep 21 2024
MATHEMATICA
Select[Range[3457], Mod[2^#-2, #(#+1)/2 ]==0&] (* James C. McMahon, Sep 23 2024 *)
PROG
(Magma) [1] cat [m: m in [2..3500] | Modexp(2, m, m*(m+1) div 2) eq 2];
CROSSREFS
Supersequence of A216822, A217465, A217466 and A375792.
Sequence in context: A287940 A237349 A095082 * A265396 A216553 A250298
KEYWORD
nonn
AUTHOR
STATUS
approved