21311019997 has 2 divisors, whose sum is σ = 21311019998. Its totient is φ = 21311019996.

The previous prime is 21311019971. The next prime is 21311020039. The reversal of 21311019997 is 79991011312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21295856761 + 15163236 = 145931^2 + 3894^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21311019997 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21311019397) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10655509998 + 10655509999.

It is an arithmetic number, because the mean of its divisors is an integer number (10655509999).

Almost surely, 2^21311019997 is an apocalyptic number.

It is an amenable number.

21311019997 is a deficient number, since it is larger than the sum of its proper divisors (1).

21311019997 is an equidigital number, since it uses as much as digits as its factorization.

21311019997 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 30618, while the sum is 43.

The spelling of 21311019997 in words is "twenty-one billion, three hundred eleven million, nineteen thousand, nine hundred ninety-seven".