645561121 has 4 divisors (see below), whose sum is σ = 659296512. Its totient is φ = 631825732.

The previous prime is 645561073. The next prime is 645561131. The reversal of 645561121 is 121165546.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 645561121 - 2¹⁵ = 645528353 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (645561131) 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, 6867625 + ... + 6867718.

It is an arithmetic number, because the mean of its divisors is an integer number (164824128).

Almost surely, 2^645561121 is an apocalyptic number.

It is an amenable number.

645561121 is a deficient number, since it is larger than the sum of its proper divisors (13735391).

645561121 is a wasteful number, since it uses less digits than its factorization.

645561121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13735390.

The product of its digits is 7200, while the sum is 31.

The square root of 645561121 is about 25407.8948557333. The cubic root of 645561121 is about 864.2627377567.

It can be divided in two parts, 6455 and 61121, that added together give a palindrome (67576).

The spelling of 645561121 in words is "six hundred forty-five million, five hundred sixty-one thousand, one hundred twenty-one".