31720981 has 2 divisors, whose sum is σ = 31720982. Its totient is φ = 31720980.

The previous prime is 31720957. The next prime is 31720991. The reversal of 31720981 is 18902713.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 31460881 + 260100 = 5609^2 + 510^2 .

It is a cyclic number.

It is not a de Polignac number, because 31720981 - 2²¹ = 29623829 is a prime.

It is a super-2 number, since 2×31720981² = 2012441271204722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (31720991) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15860490 + 15860491.

It is an arithmetic number, because the mean of its divisors is an integer number (15860491).

Almost surely, 2^31720981 is an apocalyptic number.

It is an amenable number.

31720981 is a deficient number, since it is larger than the sum of its proper divisors (1).

31720981 is an equidigital number, since it uses as much as digits as its factorization.

31720981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3024, while the sum is 31.

The square root of 31720981 is about 5632.1382262867. The cubic root of 31720981 is about 316.5547757354.

The spelling of 31720981 in words is "thirty-one million, seven hundred twenty thousand, nine hundred eighty-one".