21953778 has 128 divisors (see below), whose sum is σ = 59996160. Its totient is φ = 5184000.

The previous prime is 21953777. The next prime is 21953791. The reversal of 21953778 is 87735912.

It is a Harshad number since it is a multiple of its sum of digits (42).

Its product of digits (105840) is a multiple of the sum of its prime divisors (144).

It is not an unprimeable number, because it can be changed into a prime (21953777) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 359868 + ... + 359928.

It is an arithmetic number, because the mean of its divisors is an integer number (468720).

Almost surely, 2^21953778 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21953778, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29998080).

21953778 is an abundant number, since it is smaller than the sum of its proper divisors (38042382).

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

21953778 is a wasteful number, since it uses less digits than its factorization.

21953778 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 144.

The product of its digits is 105840, while the sum is 42.

The square root of 21953778 is about 4685.4858872907. The cubic root of 21953778 is about 280.0075593197.

The spelling of 21953778 in words is "twenty-one million, nine hundred fifty-three thousand, seven hundred seventy-eight".