21729687 has 24 divisors (see below), whose sum is σ = 35174016. Its totient is φ = 11875248.

The previous prime is 21729683. The next prime is 21729709. The reversal of 21729687 is 78692712.

It is not a de Polignac number, because 21729687 - 2² = 21729683 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21729683) 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 23 ways as a sum of consecutive naturals, for example, 168 + ... + 6594.

It is an arithmetic number, because the mean of its divisors is an integer number (1465584).

Almost surely, 2^21729687 is an apocalyptic number.

21729687 is a deficient number, since it is larger than the sum of its proper divisors (13444329).

21729687 is a wasteful number, since it uses less digits than its factorization.

21729687 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6467 (or 6460 counting only the distinct ones).

The product of its digits is 84672, while the sum is 42.

The square root of 21729687 is about 4661.5112356402. The cubic root of 21729687 is about 279.0515828110.

The spelling of 21729687 in words is "twenty-one million, seven hundred twenty-nine thousand, six hundred eighty-seven".