21257644 has 6 divisors (see below), whose sum is σ = 37200884. Its totient is φ = 10628820.

The previous prime is 21257581. The next prime is 21257651. The reversal of 21257644 is 44675212.

It is a zygodrome in base 3.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2657202 + ... + 2657209.

Almost surely, 2^21257644 is an apocalyptic number.

It is an amenable number.

21257644 is a deficient number, since it is larger than the sum of its proper divisors (15943240).

21257644 is a wasteful number, since it uses less digits than its factorization.

21257644 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5314415 (or 5314413 counting only the distinct ones).

The product of its digits is 13440, while the sum is 31.

The square root of 21257644 is about 4610.6012623084. The cubic root of 21257644 is about 277.0161207368.

It can be divided in two parts, 2125764 and 4, that multiplied together give a 4-th power (8503056 = 54⁴).

The spelling of 21257644 in words is "twenty-one million, two hundred fifty-seven thousand, six hundred forty-four".