A Thābit ibn Qurra number, sometimes called a 321-number, is a number of the form
for a nonnegative integer. The first few for , 1, ... are 2, 5, 11, 23, 47, 95, 191, 383, 767, ... (OEIS
A055010, whose term at index is ).
Riesel, H. "Några stora primtal." Elementa39, 258-260, 1956.Riesel, H. "Lucasian Criteria for the Primality of
."
Math. Comput.23, 869-875, 1969.Sloane, N. J. A.
Sequence A055010 in "The On-Line Encyclopedia
of Integer Sequences."
for a nonnegative integer 
. The first few for 
, 1, ... are 2, 5, 11, 23, 47, 95, 191, 383, 767, ... (OEIS
A055010, whose term at index 
is 
).
such that 
is a composite number for every positive
integer 
(Riesel 1956, p. 260). Numbers 
with this property are called Riesel
numbers.
."
Math. Comput. 23, 869-875, 1969.Sloane, N. J. A.
Sequence