21161756 has 48 divisors (see below), whose sum is σ = 46620672. Its totient is φ = 8164800.

The previous prime is 21161737. The next prime is 21161761. The reversal of 21161756 is 65716112.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 38846 + ... + 39386.

It is an arithmetic number, because the mean of its divisors is an integer number (971264).

Almost surely, 2^21161756 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21161756, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23310336).

21161756 is an abundant number, since it is smaller than the sum of its proper divisors (25458916).

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

21161756 is a wasteful number, since it uses less digits than its factorization.

21161756 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 690 (or 688 counting only the distinct ones).

The product of its digits is 2520, while the sum is 29.

The square root of 21161756 is about 4600.1908656055. The cubic root of 21161756 is about 276.5989757140.

Adding to 21161756 its reverse (65716112), we get a palindrome (86877868).

The spelling of 21161756 in words is "twenty-one million, one hundred sixty-one thousand, seven hundred fifty-six".