21408036 has 48 divisors (see below), whose sum is σ = 54331200. Its totient is φ = 6521472.

The previous prime is 21408029. The next prime is 21408047. The reversal of 21408036 is 63080412.

It is a happy number.

It is a junction number, because it is equal to n+sod(n) for n = 21407997 and 21408015.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 16375 + ... + 17633.

It is an arithmetic number, because the mean of its divisors is an integer number (1131900).

Almost surely, 2^21408036 is an apocalyptic number.

21408036 is a gapful number since it is divisible by the number (26) 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 21408036, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27165600).

21408036 is an abundant number, since it is smaller than the sum of its proper divisors (32923164).

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

21408036 is a wasteful number, since it uses less digits than its factorization.

21408036 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1388 (or 1386 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 24.

The square root of 21408036 is about 4626.8818874054. The cubic root of 21408036 is about 277.6678572138.

Adding to 21408036 its reverse (63080412), we get a palindrome (84488448).

The spelling of 21408036 in words is "twenty-one million, four hundred eight thousand, thirty-six".