21103606721 has 2 divisors, whose sum is σ = 21103606722. Its totient is φ = 21103606720.

The previous prime is 21103606697. The next prime is 21103606729. The reversal of 21103606721 is 12760630112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15525160000 + 5578446721 = 124600^2 + 74689^2 .

It is a cyclic number.

It is not a de Polignac number, because 21103606721 - 2¹⁴ = 21103590337 is a prime.

It is not a weakly prime, because it can be changed into another prime (21103606729) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10551803360 + 10551803361.

It is an arithmetic number, because the mean of its divisors is an integer number (10551803361).

Almost surely, 2^21103606721 is an apocalyptic number.

It is an amenable number.

21103606721 is a deficient number, since it is larger than the sum of its proper divisors (1).

21103606721 is an equidigital number, since it uses as much as digits as its factorization.

21103606721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3024, while the sum is 29.

The spelling of 21103606721 in words is "twenty-one billion, one hundred three million, six hundred six thousand, seven hundred twenty-one".