21236240 has 40 divisors (see below), whose sum is σ = 50972928. Its totient is φ = 8219520.

The previous prime is 21236239. The next prime is 21236249. The reversal of 21236240 is 4263212.

It is a tau number, because it is divible by the number of its divisors (40).

It is a Harshad number since it is a multiple of its sum of digits (20).

It is not an unprimeable number, because it can be changed into a prime (21236249) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1802 + ... + 6761.

Almost surely, 2^21236240 is an apocalyptic number.

21236240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21236240 is an abundant number, since it is smaller than the sum of its proper divisors (29736688).

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

21236240 is a wasteful number, since it uses less digits than its factorization.

21236240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8607 (or 8601 counting only the distinct ones).

The product of its (nonzero) digits is 576, while the sum is 20.

The square root of 21236240 is about 4608.2795054120. The cubic root of 21236240 is about 276.9231150681.

Adding to 21236240 its reverse (4263212), we get a palindrome (25499452).

The spelling of 21236240 in words is "twenty-one million, two hundred thirty-six thousand, two hundred forty".