645187861 has 2 divisors, whose sum is σ = 645187862. Its totient is φ = 645187860.

The previous prime is 645187843. The next prime is 645187891. The reversal of 645187861 is 168781546.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 632271025 + 12916836 = 25145^2 + 3594^2 .

It is a cyclic number.

It is not a de Polignac number, because 645187861 - 2²¹ = 643090709 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (645187891) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322593930 + 322593931.

It is an arithmetic number, because the mean of its divisors is an integer number (322593931).

Almost surely, 2^645187861 is an apocalyptic number.

It is an amenable number.

645187861 is a deficient number, since it is larger than the sum of its proper divisors (1).

645187861 is an equidigital number, since it uses as much as digits as its factorization.

645187861 is an evil number, because the sum of its binary digits is even.

The product of its digits is 322560, while the sum is 46.

The square root of 645187861 is about 25400.5484389609. The cubic root of 645187861 is about 864.0961349398.

The spelling of 645187861 in words is "six hundred forty-five million, one hundred eighty-seven thousand, eight hundred sixty-one".