21211997 has 2 divisors, whose sum is σ = 21211998. Its totient is φ = 21211996.

The previous prime is 21211979. The next prime is 21212017. The reversal of 21211997 is 79911212.

Together with previous prime (21211979) 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., 20921476 + 290521 = 4574^2 + 539^2 .

It is a cyclic number.

It is not a de Polignac number, because 21211997 - 2¹⁴ = 21195613 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21216997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10605998 + 10605999.

It is an arithmetic number, because the mean of its divisors is an integer number (10605999).

Almost surely, 2^21211997 is an apocalyptic number.

It is an amenable number.

21211997 is a deficient number, since it is larger than the sum of its proper divisors (1).

21211997 is an equidigital number, since it uses as much as digits as its factorization.

21211997 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2268, while the sum is 32.

The square root of 21211997 is about 4605.6483799787. The cubic root of 21211997 is about 276.8176977349.

The spelling of 21211997 in words is "twenty-one million, two hundred eleven thousand, nine hundred ninety-seven".