21308644 has 12 divisors (see below), whose sum is σ = 42617344. Its totient is φ = 9132264.

The previous prime is 21308629. The next prime is 21308653. The reversal of 21308644 is 44680312.

21308644 is an admirable number.

It is a hoax number, since the sum of its digits (28) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (28), and also a Moran number because the ratio is a prime number: 761023 = 21308644 / (2 + 1 + 3 + 0 + 8 + 6 + 4 + 4).

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 380484 + ... + 380539.

Almost surely, 2^21308644 is an apocalyptic number.

It is an amenable number.

21308644 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

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

21308644 is a wasteful number, since it uses less digits than its factorization.

21308644 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 761034 (or 761032 counting only the distinct ones).

The product of its (nonzero) digits is 4608, while the sum is 28.

The square root of 21308644 is about 4616.1286810487. The cubic root of 21308644 is about 277.2374770169.

Adding to 21308644 its reverse (44680312), we get a palindrome (65988956).

It can be divided in two parts, 21308 and 644, that added together give a cube (21952 = 28³).

The spelling of 21308644 in words is "twenty-one million, three hundred eight thousand, six hundred forty-four".