21621756 has 96 divisors (see below), whose sum is σ = 59609088. Its totient is φ = 6036480.

The previous prime is 21621737. The next prime is 21621757. The reversal of 21621756 is 65712612.

It is a zygodrome in base 11.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21621757) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 82081 + ... + 82343.

It is an arithmetic number, because the mean of its divisors is an integer number (620928).

Almost surely, 2^21621756 is an apocalyptic number.

21621756 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21621756, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29804544).

21621756 is an abundant number, since it is smaller than the sum of its proper divisors (37987332).

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

21621756 is a wasteful number, since it uses less digits than its factorization.

21621756 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 331 (or 329 counting only the distinct ones).

The product of its digits is 5040, while the sum is 30.

The square root of 21621756 is about 4649.9199993118. The cubic root of 21621756 is about 278.5888008702.

The spelling of 21621756 in words is "twenty-one million, six hundred twenty-one thousand, seven hundred fifty-six".