A congruum is a positive integer 
that is the common difference
of an arithmetic progression of three square numbers. Equivalently, the congruum
problem has integer solutions satisfying
 |
and
 |
The first congrua are 24, 96, 120, 216, 240, 336, 384, 480, 600, 720, ... (OEIS A256418). For example, 
and 
. If 
is a congruum, then so is 
for every positive integer 
, obtained by multiplying 
, 
,
and 
by 
.
