21311331997 has 2 divisors, whose sum is σ = 21311331998. Its totient is φ = 21311331996.

The previous prime is 21311331947. The next prime is 21311332057. The reversal of 21311331997 is 79913311312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20716996356 + 594335641 = 143934^2 + 24379^2 .

It is a cyclic number.

It is not a de Polignac number, because 21311331997 - 2²⁷ = 21177114269 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21311331947) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10655665998 + 10655665999.

It is an arithmetic number, because the mean of its divisors is an integer number (10655665999).

Almost surely, 2^21311331997 is an apocalyptic number.

It is an amenable number.

21311331997 is a deficient number, since it is larger than the sum of its proper divisors (1).

21311331997 is an equidigital number, since it uses as much as digits as its factorization.

21311331997 is an evil number, because the sum of its binary digits is even.

The product of its digits is 30618, while the sum is 40.

The spelling of 21311331997 in words is "twenty-one billion, three hundred eleven million, three hundred thirty-one thousand, nine hundred ninety-seven".