21387280 has 20 divisors (see below), whose sum is σ = 49725612. Its totient is φ = 8554880.

The previous prime is 21387277. The next prime is 21387287. The reversal of 21387280 is 8278312.

It can be written as a sum of positive squares in 2 ways, for example, as 15492096 + 5895184 = 3936^2 + 2428^2 .

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 (21387287) 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, 133591 + ... + 133750.

Almost surely, 2^21387280 is an apocalyptic number.

21387280 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21387280 is an abundant number, since it is smaller than the sum of its proper divisors (28338332).

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

21387280 is a wasteful number, since it uses less digits than its factorization.

21387280 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 267354 (or 267348 counting only the distinct ones).

The product of its (nonzero) digits is 5376, while the sum is 31.

The square root of 21387280 is about 4624.6383642400. The cubic root of 21387280 is about 277.5780912707.

The spelling of 21387280 in words is "twenty-one million, three hundred eighty-seven thousand, two hundred eighty".