21287280 has 80 divisors (see below), whose sum is σ = 75423744. Its totient is φ = 4865280.

The previous prime is 21287269. The next prime is 21287303. The reversal of 21287280 is 8278212.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (80).

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

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, 4656 + ... + 8015.

Almost surely, 2^21287280 is an apocalyptic number.

21287280 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21287280 is an abundant number, since it is smaller than the sum of its proper divisors (54136464).

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

21287280 is a wasteful number, since it uses less digits than its factorization.

21287280 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12694 (or 12688 counting only the distinct ones).

The product of its (nonzero) digits is 3584, while the sum is 30.

The square root of 21287280 is about 4613.8140404659. The cubic root of 21287280 is about 277.1447934719.

The spelling of 21287280 in words is "twenty-one million, two hundred eighty-seven thousand, two hundred eighty".