21656557799 has 2 divisors, whose sum is σ = 21656557800. Its totient is φ = 21656557798.

The previous prime is 21656557781. The next prime is 21656557837. The reversal of 21656557799 is 99775565612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21656557799 - 2¹² = 21656553703 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21656551799) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10828278899 + 10828278900.

It is an arithmetic number, because the mean of its divisors is an integer number (10828278900).

Almost surely, 2^21656557799 is an apocalyptic number.

21656557799 is a deficient number, since it is larger than the sum of its proper divisors (1).

21656557799 is an equidigital number, since it uses as much as digits as its factorization.

21656557799 is an evil number, because the sum of its binary digits is even.

The product of its digits is 35721000, while the sum is 62.

The spelling of 21656557799 in words is "twenty-one billion, six hundred fifty-six million, five hundred fifty-seven thousand, seven hundred ninety-nine".