31678721 has 4 divisors (see below), whose sum is σ = 31690032. Its totient is φ = 31667412.

The previous prime is 31678657. The next prime is 31678781. The reversal of 31678721 is 12787613.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 31678721 - 2⁶ = 31678657 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (31678781) 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, 2006 + ... + 8208.

It is an arithmetic number, because the mean of its divisors is an integer number (7922508).

Almost surely, 2^31678721 is an apocalyptic number.

It is an amenable number.

31678721 is a deficient number, since it is larger than the sum of its proper divisors (11311).

31678721 is an equidigital number, since it uses as much as digits as its factorization.

31678721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11310.

The product of its digits is 14112, while the sum is 35.

The square root of 31678721 is about 5628.3852924262. The cubic root of 31678721 is about 316.4141374834.

The spelling of 31678721 in words is "thirty-one million, six hundred seventy-eight thousand, seven hundred twenty-one".