21905949 has 12 divisors (see below), whose sum is σ = 31628256. Its totient is φ = 13480272.

The previous prime is 21905929. The next prime is 21905953. The reversal of 21905949 is 94950912.

It is not a de Polignac number, because 21905949 - 2¹¹ = 21903901 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (39).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21905929) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 21097 + ... + 22110.

It is an arithmetic number, because the mean of its divisors is an integer number (2635688).

Almost surely, 2^21905949 is an apocalyptic number.

It is an amenable number.

21905949 is a deficient number, since it is larger than the sum of its proper divisors (9722307).

21905949 is a wasteful number, since it uses less digits than its factorization.

21905949 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 43236 (or 43223 counting only the distinct ones).

The product of its (nonzero) digits is 29160, while the sum is 39.

The square root of 21905949 is about 4680.3791513082. The cubic root of 21905949 is about 279.8040678589.

The spelling of 21905949 in words is "twenty-one million, nine hundred five thousand, nine hundred forty-nine".