21311766 has 72 divisors (see below), whose sum is σ = 54614664. Its totient is φ = 5987520.

The previous prime is 21311747. The next prime is 21311767. The reversal of 21311766 is 66711312.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21311767) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 64221 + ... + 64551.

It is an arithmetic number, because the mean of its divisors is an integer number (758537).

Almost surely, 2^21311766 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21311766, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27307332).

21311766 is an abundant number, since it is smaller than the sum of its proper divisors (33302898).

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

21311766 is a wasteful number, since it uses less digits than its factorization.

21311766 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 426 (or 416 counting only the distinct ones).

The product of its digits is 1512, while the sum is 27.

The square root of 21311766 is about 4616.4668308134. The cubic root of 21311766 is about 277.2510160160.

The spelling of 21311766 in words is "twenty-one million, three hundred eleven thousand, seven hundred sixty-six".