645521 has 2 divisors, whose sum is σ = 645522. Its totient is φ = 645520.

The previous prime is 645503. The next prime is 645527. The reversal of 645521 is 125546.

645521 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 384400 + 261121 = 620^2 + 511^2 .

It is a cyclic number.

It is not a de Polignac number, because 645521 - 2¹⁴ = 629137 is a prime.

It is a super-2 number, since 2×645521² = 833394722882, which contains 22 as substring.

It is a Chen prime.

It is equal to p₅₂₄₈₄ and since 645521 and 52484 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (645527) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322760 + 322761.

It is an arithmetic number, because the mean of its divisors is an integer number (322761).

2⁶⁴⁵⁵²¹ is an apocalyptic number.

It is an amenable number.

645521 is a deficient number, since it is larger than the sum of its proper divisors (1).

645521 is an equidigital number, since it uses as much as digits as its factorization.

645521 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1200, while the sum is 23.

The square root of 645521 is about 803.4432151683. The cubic root of 645521 is about 86.4244833021.

The spelling of 645521 in words is "six hundred forty-five thousand, five hundred twenty-one".