645216251 has 4 divisors (see below), whose sum is σ = 645635952. Its totient is φ = 644796552.

The previous prime is 645216241. The next prime is 645216259. The reversal of 645216251 is 152612546.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 645216251 - 2¹⁰ = 645215227 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (645216259) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 207536 + ... + 210621.

It is an arithmetic number, because the mean of its divisors is an integer number (161408988).

Almost surely, 2^645216251 is an apocalyptic number.

645216251 is a deficient number, since it is larger than the sum of its proper divisors (419701).

645216251 is a wasteful number, since it uses less digits than its factorization.

645216251 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 419700.

The product of its digits is 14400, while the sum is 32.

The square root of 645216251 is about 25401.1072790144. The cubic root of 645216251 is about 864.1088089380.

Adding to 645216251 its reverse (152612546), we get a palindrome (797828797).

The spelling of 645216251 in words is "six hundred forty-five million, two hundred sixteen thousand, two hundred fifty-one".