21288690 has 64 divisors (see below), whose sum is σ = 58331520. Its totient is φ = 5520960.

The previous prime is 21288671. The next prime is 21288691. The reversal of 21288690 is 9688212.

It is a super-2 number, since 2×21288690² = 906416643832200, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21288691) 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 31 ways as a sum of consecutive naturals, for example, 8925 + ... + 11055.

It is an arithmetic number, because the mean of its divisors is an integer number (911430).

Almost surely, 2^21288690 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21288690, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29165760).

21288690 is an abundant number, since it is smaller than the sum of its proper divisors (37042830).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21288690 is a wasteful number, since it uses less digits than its factorization.

21288690 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2184 (or 2178 counting only the distinct ones).

The product of its (nonzero) digits is 13824, while the sum is 36.

The square root of 21288690 is about 4613.9668399329. The cubic root of 21288690 is about 277.1509123926.

The spelling of 21288690 in words is "twenty-one million, two hundred eighty-eight thousand, six hundred ninety".