21215400 has 96 divisors (see below), whose sum is σ = 69266400. Its totient is φ = 5356800.

The previous prime is 21215399. The next prime is 21215401. The reversal of 21215400 is 451212.

It is an interprime number because it is at equal distance from previous prime (21215399) and next prime (21215401).

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a self number, because there is not a number n which added to its sum of digits gives 21215400.

It is not an unprimeable number, because it can be changed into a prime (21215401) 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, 10470 + ... + 12330.

It is an arithmetic number, because the mean of its divisors is an integer number (721525).

Almost surely, 2^21215400 is an apocalyptic number.

21215400 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 21215400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34633200).

21215400 is an abundant number, since it is smaller than the sum of its proper divisors (48051000).

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

21215400 is a wasteful number, since it uses less digits than its factorization.

21215400 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1899 (or 1890 counting only the distinct ones).

The product of its (nonzero) digits is 80, while the sum is 15.

The square root of 21215400 is about 4606.0178028314. The cubic root of 21215400 is about 276.8325000542.

Adding to 21215400 its reverse (451212), we get a palindrome (21666612).

The spelling of 21215400 in words is "twenty-one million, two hundred fifteen thousand, four hundred".