21821691 has 8 divisors (see below), whose sum is σ = 29362960. Its totient is φ = 14414112.

The previous prime is 21821669. The next prime is 21821707. The reversal of 21821691 is 19612812.

It is a happy number.

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

It is not a de Polignac number, because 21821691 - 2¹¹ = 21819643 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21821621) 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, 33040 + ... + 33693.

It is an arithmetic number, because the mean of its divisors is an integer number (3670370).

Almost surely, 2^21821691 is an apocalyptic number.

21821691 is a deficient number, since it is larger than the sum of its proper divisors (7541269).

21821691 is a wasteful number, since it uses less digits than its factorization.

21821691 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 66845.

The product of its digits is 1728, while the sum is 30.

The square root of 21821691 is about 4671.3692853381. The cubic root of 21821691 is about 279.4448652399. Note that the first 3 decimals are identical.

The spelling of 21821691 in words is "twenty-one million, eight hundred twenty-one thousand, six hundred ninety-one".