31391561 has 4 divisors (see below), whose sum is σ = 32404224. Its totient is φ = 30378900.

The previous prime is 31391539. The next prime is 31391567. The reversal of 31391561 is 16519313.

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 31391561 - 2⁶ = 31391497 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (31391567) 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, 506285 + ... + 506346.

It is an arithmetic number, because the mean of its divisors is an integer number (8101056).

Almost surely, 2^31391561 is an apocalyptic number.

31391561 is a gapful number since it is divisible by the number (31) formed by its first and last digit.

It is an amenable number.

31391561 is a deficient number, since it is larger than the sum of its proper divisors (1012663).

31391561 is a wasteful number, since it uses less digits than its factorization.

31391561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1012662.

The product of its digits is 2430, while the sum is 29.

The square root of 31391561 is about 5602.8172377831. The cubic root of 31391561 is about 315.4551612610.

The spelling of 31391561 in words is "thirty-one million, three hundred ninety-one thousand, five hundred sixty-one".