21400428 has 48 divisors (see below), whose sum is σ = 57625344. Its totient is φ = 6054720.

The previous prime is 21400417. The next prime is 21400429. The reversal of 21400428 is 82400412.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is not an unprimeable number, because it can be changed into a prime (21400429) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7798 + ... + 10178.

It is an arithmetic number, because the mean of its divisors is an integer number (1200528).

Almost surely, 2^21400428 is an apocalyptic number.

21400428 is a gapful number since it is divisible by the number (28) 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 21400428, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28812672).

21400428 is an abundant number, since it is smaller than the sum of its proper divisors (36224916).

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

21400428 is a wasteful number, since it uses less digits than its factorization.

21400428 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2502 (or 2500 counting only the distinct ones).

The product of its (nonzero) digits is 512, while the sum is 21.

The square root of 21400428 is about 4626.0596623909. The cubic root of 21400428 is about 277.6349607296.

The spelling of 21400428 in words is "twenty-one million, four hundred thousand, four hundred twenty-eight".