21756906 has 48 divisors (see below), whose sum is σ = 50496264. Its totient is φ = 6746112.

The previous prime is 21756901. The next prime is 21756949. The reversal of 21756906 is 60965712.

21756906 is a nontrivial binomial coefficient, being equal to C(6597, 2).

It can be written as a sum of positive squares in 4 ways, for example, as 21706281 + 50625 = 4659^2 + 225^2 .

It is not an unprimeable number, because it can be changed into a prime (21756901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 29316 + ... + 30048.

Almost surely, 2^21756906 is an apocalyptic number.

21756906 is the 6596-th triangular number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21756906, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25248132).

21756906 is an abundant number, since it is smaller than the sum of its proper divisors (28739358).

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

21756906 is a wasteful number, since it uses less digits than its factorization.

21756906 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 855 (or 852 counting only the distinct ones).

The product of its (nonzero) digits is 22680, while the sum is 36.

The square root of 21756906 is about 4664.4298686978. The cubic root of 21756906 is about 279.1680492197.

The spelling of 21756906 in words is "twenty-one million, seven hundred fifty-six thousand, nine hundred six".