21771666 has 80 divisors (see below), whose sum is σ = 56732544. Its totient is φ = 6111936.

The previous prime is 21771619. The next prime is 21771671. The reversal of 21771666 is 66617712.

It is a nude number because it is divisible by every one of its digits.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21771666.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 82651 + ... + 82913.

Almost surely, 2^21771666 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21771666, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28366272).

21771666 is an abundant number, since it is smaller than the sum of its proper divisors (34960878).

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

21771666 is a wasteful number, since it uses less digits than its factorization.

21771666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 357 (or 348 counting only the distinct ones).

The product of its digits is 21168, while the sum is 36.

The square root of 21771666 is about 4666.0117873833. The cubic root of 21771666 is about 279.2311646425.

The spelling of 21771666 in words is "twenty-one million, seven hundred seventy-one thousand, six hundred sixty-six".