64631781 has 6 divisors (see below), whose sum is σ = 93357030. Its totient is φ = 43087848.

The previous prime is 64631767. The next prime is 64631813. The reversal of 64631781 is 18713646.

64631781 is a `hidden beast` number, since 646 + 3 + 1 + 7 + 8 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 36180225 + 28451556 = 6015^2 + 5334^2 .

It is not a de Polignac number, because 64631781 - 2⁷ = 64631653 is a prime.

It is a super-2 number, since 2×64631781² = 8354534230463922, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (64631701) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 3590646 + ... + 3590663.

It is an arithmetic number, because the mean of its divisors is an integer number (15559505).

Almost surely, 2^64631781 is an apocalyptic number.

It is an amenable number.

64631781 is a deficient number, since it is larger than the sum of its proper divisors (28725249).

64631781 is a wasteful number, since it uses less digits than its factorization.

64631781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7181315 (or 7181312 counting only the distinct ones).

The product of its digits is 24192, while the sum is 36.

The square root of 64631781 is about 8039.3893424812. The cubic root of 64631781 is about 401.3119029891.

The spelling of 64631781 in words is "sixty-four million, six hundred thirty-one thousand, seven hundred eighty-one".