64809981 has 6 divisors (see below), whose sum is σ = 93614430. Its totient is φ = 43206648.

The previous prime is 64809973. The next prime is 64809989. The reversal of 64809981 is 18990846.

64809981 is a `hidden beast` number, since 6 + 480 + 99 + 81 = 666.

It is an interprime number because it is at equal distance from previous prime (64809973) and next prime (64809989).

It can be written as a sum of positive squares in only one way, i.e., 59814756 + 4995225 = 7734^2 + 2235^2 .

It is not a de Polignac number, because 64809981 - 2³ = 64809973 is a prime.

It is a super-2 number, since 2×64809981² = 8400667274440722, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (64809989) 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, 3600546 + ... + 3600563.

It is an arithmetic number, because the mean of its divisors is an integer number (15602405).

Almost surely, 2^64809981 is an apocalyptic number.

It is an amenable number.

64809981 is a deficient number, since it is larger than the sum of its proper divisors (28804449).

64809981 is a wasteful number, since it uses less digits than its factorization.

64809981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7201115 (or 7201112 counting only the distinct ones).

The product of its (nonzero) digits is 124416, while the sum is 45.

The square root of 64809981 is about 8050.4646449755. The cubic root of 64809981 is about 401.6803912445.

It can be divided in two parts, 6480 and 9981, that added together give a palindrome (16461).

The spelling of 64809981 in words is "sixty-four million, eight hundred nine thousand, nine hundred eighty-one".