21319997 has 2 divisors, whose sum is σ = 21319998. Its totient is φ = 21319996.

The previous prime is 21319981. The next prime is 21320021. The reversal of 21319997 is 79991312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19412836 + 1907161 = 4406^2 + 1381^2 .

It is a cyclic number.

It is not a de Polignac number, because 21319997 - 2⁴ = 21319981 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 (21319937) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10659998 + 10659999.

It is an arithmetic number, because the mean of its divisors is an integer number (10659999).

Almost surely, 2^21319997 is an apocalyptic number.

It is an amenable number.

21319997 is a deficient number, since it is larger than the sum of its proper divisors (1).

21319997 is an equidigital number, since it uses as much as digits as its factorization.

21319997 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 21319997 is about 4617.3582273850. The cubic root of 21319997 is about 277.2867045864.

The spelling of 21319997 in words is "twenty-one million, three hundred nineteen thousand, nine hundred ninety-seven".