644447domain: NPropertiesPrimalityPrimeyesAppears in sequencesPrimes such that the outer 2 digits are n and n+1 and all inner digits are 4, where 0 < n < 9.at n=3A108821Number of planar n X n X n binary triangular grids symmetric under 120 degree rotation with no more than 4 ones in any 5 X 5 X 5 subtriangle.at n=13A153935Prime numbersat n=52400