21955905 has 24 divisors (see below), whose sum is σ = 39287040. Its totient is φ = 11331360.

The previous prime is 21955889. The next prime is 21955919. The reversal of 21955905 is 50955912.

It is not a de Polignac number, because 21955905 - 2⁴ = 21955889 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21955905.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 6475 + ... + 9264.

It is an arithmetic number, because the mean of its divisors is an integer number (1636960).

Almost surely, 2^21955905 is an apocalyptic number.

It is an amenable number.

21955905 is a deficient number, since it is larger than the sum of its proper divisors (17331135).

21955905 is a wasteful number, since it uses less digits than its factorization.

21955905 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15781 (or 15778 counting only the distinct ones).

The product of its (nonzero) digits is 20250, while the sum is 36.

The square root of 21955905 is about 4685.7128593203. The cubic root of 21955905 is about 280.0166019068.

It can be divided in two parts, 2195 and 5905, that added together give a square (8100 = 90²).

The spelling of 21955905 in words is "twenty-one million, nine hundred fifty-five thousand, nine hundred five".