21219997 has 2 divisors, whose sum is σ = 21219998. Its totient is φ = 21219996.

The previous prime is 21219977. The next prime is 21220019. The reversal of 21219997 is 79991212.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21215236 + 4761 = 4606^2 + 69^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21219997 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21219917) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10609998 + 10609999.

It is an arithmetic number, because the mean of its divisors is an integer number (10609999).

Almost surely, 2^21219997 is an apocalyptic number.

It is an amenable number.

21219997 is a deficient number, since it is larger than the sum of its proper divisors (1).

21219997 is an equidigital number, since it uses as much as digits as its factorization.

21219997 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 20412, while the sum is 40.

The square root of 21219997 is about 4606.5167968868. The cubic root of 21219997 is about 276.8524935039.

The spelling of 21219997 in words is "twenty-one million, two hundred nineteen thousand, nine hundred ninety-seven".