21311221397 has 2 divisors, whose sum is σ = 21311221398. Its totient is φ = 21311221396.

The previous prime is 21311221381. The next prime is 21311221441. The reversal of 21311221397 is 79312211312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15125556196 + 6185665201 = 122986^2 + 78649^2 .

It is a cyclic number.

It is not a de Polignac number, because 21311221397 - 2⁴ = 21311221381 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21311221697) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10655610698 + 10655610699.

It is an arithmetic number, because the mean of its divisors is an integer number (10655610699).

Almost surely, 2^21311221397 is an apocalyptic number.

It is an amenable number.

21311221397 is a deficient number, since it is larger than the sum of its proper divisors (1).

21311221397 is an equidigital number, since it uses as much as digits as its factorization.

21311221397 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4536, while the sum is 32.

The spelling of 21311221397 in words is "twenty-one billion, three hundred eleven million, two hundred twenty-one thousand, three hundred ninety-seven".