21427969721 has 2 divisors, whose sum is σ = 21427969722. Its totient is φ = 21427969720.

The previous prime is 21427969697. The next prime is 21427969727. The reversal of 21427969721 is 12796972412.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20403265600 + 1024704121 = 142840^2 + 32011^2 .

It is a cyclic number.

It is not a de Polignac number, because 21427969721 - 2¹⁰ = 21427968697 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21427969721.

It is not a weakly prime, because it can be changed into another prime (21427969727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10713984860 + 10713984861.

It is an arithmetic number, because the mean of its divisors is an integer number (10713984861).

Almost surely, 2^21427969721 is an apocalyptic number.

It is an amenable number.

21427969721 is a deficient number, since it is larger than the sum of its proper divisors (1).

21427969721 is an equidigital number, since it uses as much as digits as its factorization.

21427969721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 762048, while the sum is 50.

The spelling of 21427969721 in words is "twenty-one billion, four hundred twenty-seven million, nine hundred sixty-nine thousand, seven hundred twenty-one".