646425781 has 4 divisors (see below), whose sum is σ = 647753632. Its totient is φ = 645097932.

The previous prime is 646425761. The next prime is 646425797. The reversal of 646425781 is 187524646.

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 646425781 - 2¹³ = 646417589 is a prime.

It is a super-2 number, since 2×646425781² = 835732580682919922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (646425701) 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, 663195 + ... + 664168.

It is an arithmetic number, because the mean of its divisors is an integer number (161938408).

Almost surely, 2^646425781 is an apocalyptic number.

It is an amenable number.

646425781 is a deficient number, since it is larger than the sum of its proper divisors (1327851).

646425781 is a wasteful number, since it uses less digits than its factorization.

646425781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1327850.

The product of its digits is 322560, while the sum is 43.

The square root of 646425781 is about 25424.9047392512. The cubic root of 646425781 is about 864.6484280772.

The spelling of 646425781 in words is "six hundred forty-six million, four hundred twenty-five thousand, seven hundred eighty-one".