645871381 has 2 divisors, whose sum is σ = 645871382. Its totient is φ = 645871380.

The previous prime is 645871337. The next prime is 645871399. The reversal of 645871381 is 183178546.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 482900625 + 162970756 = 21975^2 + 12766^2 .

It is a cyclic number.

It is not a de Polignac number, because 645871381 - 2⁷ = 645871253 is a prime.

It is a super-2 number, since 2×645871381² = 834299681589694322, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (645877381) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322935690 + 322935691.

It is an arithmetic number, because the mean of its divisors is an integer number (322935691).

Almost surely, 2^645871381 is an apocalyptic number.

It is an amenable number.

645871381 is a deficient number, since it is larger than the sum of its proper divisors (1).

645871381 is an equidigital number, since it uses as much as digits as its factorization.

645871381 is an evil number, because the sum of its binary digits is even.

The product of its digits is 161280, while the sum is 43.

The square root of 645871381 is about 25413.9997048871. Note that the first 3 decimals coincide. The cubic root of 645871381 is about 864.4011719561.

The spelling of 645871381 in words is "six hundred forty-five million, eight hundred seventy-one thousand, three hundred eighty-one".