21657426 has 16 divisors (see below), whose sum is σ = 49502784. Its totient is φ = 6187824.

The previous prime is 21657407. The next prime is 21657431. The reversal of 21657426 is 62475612.

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 257785 + ... + 257868.

It is an arithmetic number, because the mean of its divisors is an integer number (3093924).

Almost surely, 2^21657426 is an apocalyptic number.

21657426 is an abundant number, since it is smaller than the sum of its proper divisors (27845358).

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

21657426 is a wasteful number, since it uses less digits than its factorization.

21657426 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 515665.

The product of its digits is 20160, while the sum is 33.

The square root of 21657426 is about 4653.7539685720. The cubic root of 21657426 is about 278.7419152139.

It can be divided in two parts, 2165 and 7426, that added together give a triangular number (9591 = T₁₃₈).

The spelling of 21657426 in words is "twenty-one million, six hundred fifty-seven thousand, four hundred twenty-six".