21691538 has 8 divisors (see below), whose sum is σ = 35495280. Its totient is φ = 9859780.

The previous prime is 21691531. The next prime is 21691543. The reversal of 21691538 is 83519612.

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

It is a junction number, because it is equal to n+sod(n) for n = 21691498 and 21691507.

It is not an unprimeable number, because it can be changed into a prime (21691531) 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 3 ways as a sum of consecutive naturals, for example, 492968 + ... + 493011.

It is an arithmetic number, because the mean of its divisors is an integer number (4436910).

Almost surely, 2^21691538 is an apocalyptic number.

21691538 is a deficient number, since it is larger than the sum of its proper divisors (13803742).

21691538 is a wasteful number, since it uses less digits than its factorization.

21691538 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 985992.

The product of its digits is 12960, while the sum is 35.

The square root of 21691538 is about 4657.4175247663. The cubic root of 21691538 is about 278.8881846185. Note that the first 3 decimals are identical.

The spelling of 21691538 in words is "twenty-one million, six hundred ninety-one thousand, five hundred thirty-eight".