21288420 has 120 divisors (see below), whose sum is σ = 70802424. Its totient is φ = 5336064.

The previous prime is 21288419. The next prime is 21288461. The reversal of 21288420 is 2488212.

It can be written as a sum of positive squares in 4 ways, for example, as 876096 + 20412324 = 936^2 + 4518^2 .

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 27154 + ... + 27926.

Almost surely, 2^21288420 is an apocalyptic number.

21288420 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 21288420, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35401212).

21288420 is an abundant number, since it is smaller than the sum of its proper divisors (49514004).

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

21288420 is a wasteful number, since it uses less digits than its factorization.

21288420 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 811 (or 800 counting only the distinct ones).

The product of its (nonzero) digits is 2048, while the sum is 27.

The square root of 21288420 is about 4613.9375808522. The cubic root of 21288420 is about 277.1497407053.

The spelling of 21288420 in words is "twenty-one million, two hundred eighty-eight thousand, four hundred twenty".