10010...01001 (121-digits)

This number is a prime.

                    1 0010111111 1111111110 0011010161 1616868668 8866666611
1661616668 6661616611 1666666888 6686861611 6101011000 1111111111 1111101001

Just showing those entries submitted by 'Kalogeropoulos': (Click here to show all)

A palindromic prime that becomes a semiprime when turned upside down. Both factors are tetradic ! [Kalogeropoulos]