21656121205 has 16 divisors (see below), whose sum is σ = 26943865344. Its totient is φ = 16692143040.

The previous prime is 21656121197. The next prime is 21656121217. The reversal of 21656121205 is 50212165612.

It is not a de Polignac number, because 21656121205 - 2³ = 21656121197 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (31).

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 272562 + ... + 342931.

It is an arithmetic number, because the mean of its divisors is an integer number (1683991584).

Almost surely, 2^21656121205 is an apocalyptic number.

It is an amenable number.

21656121205 is a deficient number, since it is larger than the sum of its proper divisors (5287744139).

21656121205 is a wasteful number, since it uses less digits than its factorization.

21656121205 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 615756.

The product of its (nonzero) digits is 7200, while the sum is 31.

Adding to 21656121205 its reverse (50212165612), we get a palindrome (71868286817).

The spelling of 21656121205 in words is "twenty-one billion, six hundred fifty-six million, one hundred twenty-one thousand, two hundred five".