21663280 has 20 divisors (see below), whose sum is σ = 50367312. Its totient is φ = 8665280.

The previous prime is 21663277. The next prime is 21663281. The reversal of 21663280 is 8236612.

It is a tau number, because it is divible by the number of its divisors (20).

It is not an unprimeable number, because it can be changed into a prime (21663281) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 135316 + ... + 135475.

Almost surely, 2^21663280 is an apocalyptic number.

21663280 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21663280 is an abundant number, since it is smaller than the sum of its proper divisors (28704032).

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

21663280 is a wasteful number, since it uses less digits than its factorization.

21663280 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 270804 (or 270798 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 28.

The square root of 21663280 is about 4654.3828806835. The cubic root of 21663280 is about 278.7670275883.

Adding to 21663280 its reverse (8236612), we get a palindrome (29899892).

The spelling of 21663280 in words is "twenty-one million, six hundred sixty-three thousand, two hundred eighty".