21681335 has 24 divisors (see below), whose sum is σ = 28817376. Its totient is φ = 15566400.

The previous prime is 21681311. The next prime is 21681347. The reversal of 21681335 is 53318612.

It is not a de Polignac number, because 21681335 - 2⁶ = 21681271 is a prime.

It is a Duffinian number.

Its product of digits (4320) is a multiple of the sum of its prime divisors (216).

It is a junction number, because it is equal to n+sod(n) for n = 21681298 and 21681307.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 143510 + ... + 143660.

It is an arithmetic number, because the mean of its divisors is an integer number (1200724).

Almost surely, 2^21681335 is an apocalyptic number.

21681335 is a deficient number, since it is larger than the sum of its proper divisors (7136041).

21681335 is a wasteful number, since it uses less digits than its factorization.

21681335 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 263 (or 216 counting only the distinct ones).

The product of its digits is 4320, while the sum is 29.

The square root of 21681335 is about 4656.3220464225. The cubic root of 21681335 is about 278.8444510912.

Adding to 21681335 its reverse (53318612), we get a palindrome (74999947).

The spelling of 21681335 in words is "twenty-one million, six hundred eighty-one thousand, three hundred thirty-five".