21759966 has 72 divisors (see below), whose sum is σ = 51723360. Its totient is φ = 6606336.

The previous prime is 21759961. The next prime is 21759977. The reversal of 21759966 is 66995712.

It is a happy number.

It is a super-2 number, since 2×21759966² = 946992240642312, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21759961) 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 in 35 ways as a sum of consecutive naturals, for example, 244450 + ... + 244538.

It is an arithmetic number, because the mean of its divisors is an integer number (718380).

Almost surely, 2^21759966 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21759966, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25861680).

21759966 is an abundant number, since it is smaller than the sum of its proper divisors (29963394).

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

21759966 is a wasteful number, since it uses less digits than its factorization.

21759966 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 178 (or 158 counting only the distinct ones).

The product of its digits is 204120, while the sum is 45.

The square root of 21759966 is about 4664.7578715299. The cubic root of 21759966 is about 279.1811364694.

The spelling of 21759966 in words is "twenty-one million, seven hundred fifty-nine thousand, nine hundred sixty-six".