21655012609 has 2 divisors, whose sum is σ = 21655012610. Its totient is φ = 21655012608.

The previous prime is 21655012571. The next prime is 21655012651. The reversal of 21655012609 is 90621055612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13418905600 + 8236107009 = 115840^2 + 90753^2 .

It is a cyclic number.

It is not a de Polignac number, because 21655012609 - 2¹⁹ = 21654488321 is a prime.

It is not a weakly prime, because it can be changed into another prime (21655012679) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10827506304 + 10827506305.

It is an arithmetic number, because the mean of its divisors is an integer number (10827506305).

Almost surely, 2^21655012609 is an apocalyptic number.

It is an amenable number.

21655012609 is a deficient number, since it is larger than the sum of its proper divisors (1).

21655012609 is an equidigital number, since it uses as much as digits as its factorization.

21655012609 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 32400, while the sum is 37.

The spelling of 21655012609 in words is "twenty-one billion, six hundred fifty-five million, twelve thousand, six hundred nine".