661645625 has 20 divisors (see below), whose sum is σ = 828437940. Its totient is φ = 528264000.

The previous prime is 661645613. The next prime is 661645631. The reversal of 661645625 is 526546166.

It can be written as a sum of positive squares in 10 ways, for example, as 438651136 + 222994489 = 20944^2 + 14933^2 .

It is not a de Polignac number, because 661645625 - 2²⁴ = 644868409 is a prime.

It is a hoax number, since the sum of its digits (41) coincides with the sum of the digits of its distinct prime factors.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 517487 + ... + 518763.

It is an arithmetic number, because the mean of its divisors is an integer number (41421897).

Almost surely, 2^661645625 is an apocalyptic number.

It is an amenable number.

661645625 is a deficient number, since it is larger than the sum of its proper divisors (166792315).

661645625 is an equidigital number, since it uses as much as digits as its factorization.

661645625 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2126 (or 2111 counting only the distinct ones).

The product of its digits is 259200, while the sum is 41.

The square root of 661645625 is about 25722.4731509239. The cubic root of 661645625 is about 871.3817936972.

The spelling of 661645625 in words is "six hundred sixty-one million, six hundred forty-five thousand, six hundred twenty-five".