31721561 has 4 divisors (see below), whose sum is σ = 31766400. Its totient is φ = 31676724.

The previous prime is 31721537. The next prime is 31721567. The reversal of 31721561 is 16512713.

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.

It is a cyclic number.

It is not a de Polignac number, because 31721561 - 2⁶ = 31721497 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 31721561.

It is not an unprimeable number, because it can be changed into a prime (31721567) 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, 21341 + ... + 22778.

It is an arithmetic number, because the mean of its divisors is an integer number (7941600).

Almost surely, 2^31721561 is an apocalyptic number.

It is an amenable number.

31721561 is a deficient number, since it is larger than the sum of its proper divisors (44839).

31721561 is an equidigital number, since it uses as much as digits as its factorization.

31721561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 44838.

The product of its digits is 1260, while the sum is 26.

The square root of 31721561 is about 5632.1897162649. The cubic root of 31721561 is about 316.5567050646.

The spelling of 31721561 in words is "thirty-one million, seven hundred twenty-one thousand, five hundred sixty-one".