63691981 has 4 divisors (see below), whose sum is σ = 63710172. Its totient is φ = 63673792.

The previous prime is 63691973. The next prime is 63691993. The reversal of 63691981 is 18919636.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 44769481 + 18922500 = 6691^2 + 4350^2 .

It is a cyclic number.

It is not a de Polignac number, because 63691981 - 2³ = 63691973 is a prime.

It is a super-2 number, since 2×63691981² = 8113336887408722, 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 (63691921) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1996 + ... + 11461.

It is an arithmetic number, because the mean of its divisors is an integer number (15927543).

Almost surely, 2^63691981 is an apocalyptic number.

It is an amenable number.

63691981 is a deficient number, since it is larger than the sum of its proper divisors (18191).

63691981 is a wasteful number, since it uses less digits than its factorization.

63691981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18190.

The product of its digits is 69984, while the sum is 43.

The square root of 63691981 is about 7980.7255935786. The cubic root of 63691981 is about 399.3572615213.

The spelling of 63691981 in words is "sixty-three million, six hundred ninety-one thousand, nine hundred eighty-one".