21931997 has 2 divisors, whose sum is σ = 21931998. Its totient is φ = 21931996.

The previous prime is 21931979. The next prime is 21932039. The reversal of 21931997 is 79913912.

Together with previous prime (21931979) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21031396 + 900601 = 4586^2 + 949^2 .

It is a cyclic number.

It is not a de Polignac number, because 21931997 - 2⁶ = 21931933 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21931927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10965998 + 10965999.

It is an arithmetic number, because the mean of its divisors is an integer number (10965999).

Almost surely, 2^21931997 is an apocalyptic number.

It is an amenable number.

21931997 is a deficient number, since it is larger than the sum of its proper divisors (1).

21931997 is an equidigital number, since it uses as much as digits as its factorization.

21931997 is an evil number, because the sum of its binary digits is even.

The product of its digits is 30618, while the sum is 41.

The square root of 21931997 is about 4683.1610051332. The cubic root of 21931997 is about 279.9149273862.

The spelling of 21931997 in words is "twenty-one million, nine hundred thirty-one thousand, nine hundred ninety-seven".