645834781 has 2 divisors, whose sum is σ = 645834782. Its totient is φ = 645834780.

The previous prime is 645834769. The next prime is 645834809. The reversal of 645834781 is 187438546.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 639634681 + 6200100 = 25291^2 + 2490^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-645834781 is a prime.

It is a super-2 number, since 2×645834781² = 834205128698635922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (645534781) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322917390 + 322917391.

It is an arithmetic number, because the mean of its divisors is an integer number (322917391).

Almost surely, 2^645834781 is an apocalyptic number.

It is an amenable number.

645834781 is a deficient number, since it is larger than the sum of its proper divisors (1).

645834781 is an equidigital number, since it uses as much as digits as its factorization.

645834781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 645120, while the sum is 46.

The square root of 645834781 is about 25413.2796191283. The cubic root of 645834781 is about 864.3848437926.

The spelling of 645834781 in words is "six hundred forty-five million, eight hundred thirty-four thousand, seven hundred eighty-one".