645251440 has 80 divisors (see below), whose sum is σ = 1549900800. Its totient is φ = 249661440.

The previous prime is 645251429. The next prime is 645251443. The reversal of 645251440 is 44152546.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (80).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645251443) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 415786 + ... + 417334.

It is an arithmetic number, because the mean of its divisors is an integer number (19373760).

Almost surely, 2^645251440 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 645251440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (774950400).

645251440 is an abundant number, since it is smaller than the sum of its proper divisors (904649360).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

645251440 is a wasteful number, since it uses less digits than its factorization.

645251440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1730 (or 1724 counting only the distinct ones).

The product of its (nonzero) digits is 19200, while the sum is 31.

The square root of 645251440 is about 25401.7999362250. The cubic root of 645251440 is about 864.1245176621.

The spelling of 645251440 in words is "six hundred forty-five million, two hundred fifty-one thousand, four hundred forty".