21287400 has 96 divisors (see below), whose sum is σ = 69906240. Its totient is φ = 5340160.

The previous prime is 21287393. The next prime is 21287407. The reversal of 21287400 is 478212.

It is an interprime number because it is at equal distance from previous prime (21287393) and next prime (21287407).

It is a Harshad number since it is a multiple of its sum of digits (24).

It is not an unprimeable number, because it can be changed into a prime (21287407) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 9157 + ... + 11243.

It is an arithmetic number, because the mean of its divisors is an integer number (728190).

Almost surely, 2^21287400 is an apocalyptic number.

21287400 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 21287400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34953120).

21287400 is an abundant number, since it is smaller than the sum of its proper divisors (48618840).

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

21287400 is a wasteful number, since it uses less digits than its factorization.

21287400 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2123 (or 2114 counting only the distinct ones).

The product of its (nonzero) digits is 896, while the sum is 24.

The square root of 21287400 is about 4613.8270448728. The cubic root of 21287400 is about 277.1453142417.

The spelling of 21287400 in words is "twenty-one million, two hundred eighty-seven thousand, four hundred".