506

506 = 2 × 11 × 23. It is: a sphenic number. a square pyramidal number. a pronic number. a Harshad number. 10 506 − 10 253 − 1 {\displaystyle 10^{506}-10^{253}-1} is a prime number. Its decimal expansion is 252 nines, an eight, and 253 more nines.