31691921 has 6 divisors (see below), whose sum is σ = 32060022. Its totient is φ = 31328000.

The previous prime is 31691899. The next prime is 31691923. The reversal of 31691921 is 12919613.

It can be written as a sum of positive squares in 3 ways, for example, as 1661521 + 30030400 = 1289^2 + 5480^2 .

It is not a de Polignac number, because 31691921 - 2¹⁸ = 31429777 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (31691923) 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, 5921 + ... + 9921.

It is an arithmetic number, because the mean of its divisors is an integer number (5343337).

Almost surely, 2^31691921 is an apocalyptic number.

It is an amenable number.

31691921 is a deficient number, since it is larger than the sum of its proper divisors (368101).

31691921 is an frugal number, since it uses more digits than its factorization.

31691921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4179 (or 4090 counting only the distinct ones).

The product of its digits is 2916, while the sum is 32.

The square root of 31691921 is about 5629.5577979092. The cubic root of 31691921 is about 316.4580795629.

The spelling of 31691921 in words is "thirty-one million, six hundred ninety-one thousand, nine hundred twenty-one".