21749639 has 8 divisors (see below), whose sum is σ = 22460928. Its totient is φ = 21047040.

The previous prime is 21749621. The next prime is 21749657. The reversal of 21749639 is 93694712.

It is an interprime number because it is at equal distance from previous prime (21749621) and next prime (21749657).

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21749639 - 2¹² = 21745543 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (41).

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21749596 and 21749605.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21740639) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3119 + ... + 7295.

It is an arithmetic number, because the mean of its divisors is an integer number (2807616).

Almost surely, 2^21749639 is an apocalyptic number.

21749639 is a deficient number, since it is larger than the sum of its proper divisors (711289).

21749639 is a wasteful number, since it uses less digits than its factorization.

21749639 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4345.

The product of its digits is 81648, while the sum is 41.

The square root of 21749639 is about 4663.6508231213. The cubic root of 21749639 is about 279.1369642219.

The spelling of 21749639 in words is "twenty-one million, seven hundred forty-nine thousand, six hundred thirty-nine".