21656280 has 64 divisors (see below), whose sum is σ = 65318400. Its totient is φ = 5744000.

The previous prime is 21656279. The next prime is 21656287. The reversal of 21656280 is 8265612.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21656287) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 29761 + ... + 30479.

It is an arithmetic number, because the mean of its divisors is an integer number (1020600).

Almost surely, 2^21656280 is an apocalyptic number.

21656280 is a gapful number since it is divisible by the number (20) 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 21656280, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32659200).

21656280 is an abundant number, since it is smaller than the sum of its proper divisors (43662120).

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

21656280 is a wasteful number, since it uses less digits than its factorization.

21656280 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 984 (or 980 counting only the distinct ones).

The product of its (nonzero) digits is 5760, while the sum is 30.

The square root of 21656280 is about 4653.6308405373. The cubic root of 21656280 is about 278.7369985959.

The spelling of 21656280 in words is "twenty-one million, six hundred fifty-six thousand, two hundred eighty".