21550778 has 4 divisors (see below), whose sum is σ = 32326170. Its totient is φ = 10775388.

The previous prime is 21550777. The next prime is 21550787. The reversal of 21550778 is 87705512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 17952169 + 3598609 = 4237^2 + 1897^2 .

It is a zygodrome in base 3.

It is not an unprimeable number, because it can be changed into a prime (21550777) 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 as a sum of consecutive naturals, namely, 5387693 + ... + 5387696.

Almost surely, 2^21550778 is an apocalyptic number.

21550778 is a deficient number, since it is larger than the sum of its proper divisors (10775392).

21550778 is a wasteful number, since it uses less digits than its factorization.

21550778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10775391.

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

The square root of 21550778 is about 4642.2815511341. The cubic root of 21550778 is about 278.2836244151.

The spelling of 21550778 in words is "twenty-one million, five hundred fifty thousand, seven hundred seventy-eight".