21221739 has 48 divisors (see below), whose sum is σ = 38697984. Its totient is φ = 10886400.

The previous prime is 21221731. The next prime is 21221741. The reversal of 21221739 is 93712212.

It is not a de Polignac number, because 21221739 - 2³ = 21221731 is a prime.

It is a hoax number, since the sum of its digits (27) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (21221731) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 78174 + ... + 78444.

It is an arithmetic number, because the mean of its divisors is an integer number (806208).

Almost surely, 2^21221739 is an apocalyptic number.

21221739 is a deficient number, since it is larger than the sum of its proper divisors (17476245).

21221739 is a wasteful number, since it uses less digits than its factorization.

21221739 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 408 (or 405 counting only the distinct ones).

The product of its digits is 1512, while the sum is 27.

The square root of 21221739 is about 4606.7058729639. The cubic root of 21221739 is about 276.8600691230.

The spelling of 21221739 in words is "twenty-one million, two hundred twenty-one thousand, seven hundred thirty-nine".