21651388 has 12 divisors (see below), whose sum is σ = 41334552. Its totient is φ = 9841520.

The previous prime is 21651367. The next prime is 21651389. The reversal of 21651388 is 88315612.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21651389) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 245995 + ... + 246082.

It is an arithmetic number, because the mean of its divisors is an integer number (3444546).

Almost surely, 2^21651388 is an apocalyptic number.

It is an amenable number.

21651388 is a deficient number, since it is larger than the sum of its proper divisors (19683164).

21651388 is a wasteful number, since it uses less digits than its factorization.

21651388 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 492092 (or 492090 counting only the distinct ones).

The product of its digits is 11520, while the sum is 34.

The square root of 21651388 is about 4653.1051997564. The cubic root of 21651388 is about 278.7160087786.

It can be divided in two parts, 2165 and 1388, that added together give a palindrome (3553).

The spelling of 21651388 in words is "twenty-one million, six hundred fifty-one thousand, three hundred eighty-eight".