OFFSET
1,2
COMMENTS
a(19) = 561 is the first composite term of the sequence.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..10000
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
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Aug 29 2024
STATUS
approved