21557870 has 32 divisors (see below), whose sum is σ = 41350176. Its totient is φ = 8064000.

The previous prime is 21557843. The next prime is 21557917. The reversal of 21557870 is 7875512.

It is a self number, because there is not a number n which added to its sum of digits gives 21557870.

It is a congruent number.

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 15 ways as a sum of consecutive naturals, for example, 35570 + ... + 36170.

It is an arithmetic number, because the mean of its divisors is an integer number (1292193).

Almost surely, 2^21557870 is an apocalyptic number.

21557870 is a deficient number, since it is larger than the sum of its proper divisors (19792306).

21557870 is a wasteful number, since it uses less digits than its factorization.

21557870 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 836.

The product of its (nonzero) digits is 19600, while the sum is 35.

The square root of 21557870 is about 4643.0453368452. The cubic root of 21557870 is about 278.3141472267.

It can be divided in two parts, 215 and 57870, that added together give a palindrome (58085).

The spelling of 21557870 in words is "twenty-one million, five hundred fifty-seven thousand, eight hundred seventy".