21217280 has 120 divisors (see below), whose sum is σ = 59767008. Its totient is φ = 7077888.

The previous prime is 21217277. The next prime is 21217289. The reversal of 21217280 is 8271212.

It is a zygodrome in base 4.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21217289) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 573422 + ... + 573458.

Almost surely, 2^21217280 is an apocalyptic number.

21217280 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 21217280, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29883504).

21217280 is an abundant number, since it is smaller than the sum of its proper divisors (38549728).

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

21217280 is an frugal number, since it uses more digits than its factorization.

21217280 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 77 (or 51 counting only the distinct ones).

The product of its (nonzero) digits is 448, while the sum is 23.

The square root of 21217280 is about 4606.2218791543. The cubic root of 21217280 is about 276.8406769717.

Adding to 21217280 its reverse (8271212), we get a palindrome (29488492).

The spelling of 21217280 in words is "twenty-one million, two hundred seventeen thousand, two hundred eighty".