21661776 has 80 divisors (see below), whose sum is σ = 63745920. Its totient is φ = 7038720.

The previous prime is 21661733. The next prime is 21661781. The reversal of 21661776 is 67716612.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a self number, because there is not a number n which added to its sum of digits gives 21661776.

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, 17101 + ... + 18323.

It is an arithmetic number, because the mean of its divisors is an integer number (796824).

Almost surely, 2^21661776 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 21661776, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31872960).

21661776 is an abundant number, since it is smaller than the sum of its proper divisors (42084144).

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

21661776 is a wasteful number, since it uses less digits than its factorization.

21661776 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1281 (or 1269 counting only the distinct ones).

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

The square root of 21661776 is about 4654.2213097359. The cubic root of 21661776 is about 278.7605761905.

The spelling of 21661776 in words is "twenty-one million, six hundred sixty-one thousand, seven hundred seventy-six".