21138949 has 4 divisors (see below), whose sum is σ = 22765036. Its totient is φ = 19512864.

The previous prime is 21138937. The next prime is 21138959. The reversal of 21138949 is 94983112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 7128900 + 14010049 = 2670^2 + 3743^2 .

It is a cyclic number.

It is not a de Polignac number, because 21138949 - 2⁵ = 21138917 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21138959) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 813024 + ... + 813049.

It is an arithmetic number, because the mean of its divisors is an integer number (5691259).

Almost surely, 2^21138949 is an apocalyptic number.

It is an amenable number.

21138949 is a deficient number, since it is larger than the sum of its proper divisors (1626087).

21138949 is a wasteful number, since it uses less digits than its factorization.

21138949 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1626086.

The product of its digits is 15552, while the sum is 37.

The square root of 21138949 is about 4597.7112784515. The cubic root of 21138949 is about 276.4995721724.

The spelling of 21138949 in words is "twenty-one million, one hundred thirty-eight thousand, nine hundred forty-nine".