21394459721 has 2 divisors, whose sum is σ = 21394459722. Its totient is φ = 21394459720.

The previous prime is 21394459687. The next prime is 21394459729. The reversal of 21394459721 is 12795449312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20560405321 + 834054400 = 143389^2 + 28880^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21394459721 is a prime.

It is not a weakly prime, because it can be changed into another prime (21394459729) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10697229860 + 10697229861.

It is an arithmetic number, because the mean of its divisors is an integer number (10697229861).

Almost surely, 2^21394459721 is an apocalyptic number.

It is an amenable number.

21394459721 is a deficient number, since it is larger than the sum of its proper divisors (1).

21394459721 is an equidigital number, since it uses as much as digits as its factorization.

21394459721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 544320, while the sum is 47.

The spelling of 21394459721 in words is "twenty-one billion, three hundred ninety-four million, four hundred fifty-nine thousand, seven hundred twenty-one".