Let Q be a rational quaternion algebra with standard basis {1, i , j, k} as follows.
sage: Q.<i,j,k> = QuaternionAlgebra(-2161,-7)
sage: B =[1/2 + 2/7j + 1/14k, 1/32i + 13/32j + 19/8k, 4/7j + 1/7k, 4k]; O
Order of Quaternion Algebra (-2161, -7) with base ring Rational Field with basis (1/2 + 2/7j + 1/14k, 1/32i + 13/32j + 19/8k, 4/7j + 1/7k, 4k)
I think this (maximal Z-)order doesn't contain k but I get
sage: k in O
True
The is inconsistent with the result on Magma:
K:=Rationals();
Q<i, j,="" k="">:=QuaternionAlgebra<k|-2161, -7="">;
B:=[ 1/2 + 2/7j + 1/14k, 1/32i + 13/32j + 19/8k, 4/7j + 1/7k, 4k ];
O:= QuaternionOrder(B);
O;
k in O;
2k in O;
4k in O;
Order of Quaternion Algebra with base ring Rational Field, defined by i^2 = -2161, j^2 = -7
with coefficient ring Integer Ring
false
false
true
What is the issue here?