21991949 has 32 divisors (see below), whose sum is σ = 28089600. Its totient is φ = 16796160.

The previous prime is 21991943. The next prime is 21991951. The reversal of 21991949 is 94919912.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21991949 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21991943) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 201707 + ... + 201815.

It is an arithmetic number, because the mean of its divisors is an integer number (877800).

Almost surely, 2^21991949 is an apocalyptic number.

It is an amenable number.

21991949 is a deficient number, since it is larger than the sum of its proper divisors (6097651).

21991949 is a wasteful number, since it uses less digits than its factorization.

21991949 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 213.

The product of its digits is 52488, while the sum is 44.

The square root of 21991949 is about 4689.5574418062. The cubic root of 21991949 is about 280.1697482609.

The spelling of 21991949 in words is "twenty-one million, nine hundred ninety-one thousand, nine hundred forty-nine".