1663213domain: NAppears in sequencesBrilliant star numbers: semiprimes of the form 6n^2 - 6n + 1 such that both prime factors have the same number of decimal digits.at n=24A083749Composite numbers k == 3, 7 (mod 10) such that 5^((k-1)/2) == -1 (mod k).at n=13A375916