21231540 has 72 divisors (see below), whose sum is σ = 70263648. Its totient is φ = 5146560.

The previous prime is 21231523. The next prime is 21231547. The reversal of 21231540 is 4513212.

21231540 is a `hidden beast` number, since 2 + 123 + 1 + 540 = 666.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21231547) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 3382 + ... + 7341.

It is an arithmetic number, because the mean of its divisors is an integer number (975884).

Almost surely, 2^21231540 is an apocalyptic number.

21231540 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21231540 is an abundant number, since it is smaller than the sum of its proper divisors (49032108).

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

21231540 is a wasteful number, since it uses less digits than its factorization.

21231540 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10749 (or 10744 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 18.

The square root of 21231540 is about 4607.7695254863. The cubic root of 21231540 is about 276.9026840396.

Adding to 21231540 its reverse (4513212), we get a palindrome (25744752).

It can be divided in two parts, 2123 and 1540, that added together give a palindrome (3663).

The spelling of 21231540 in words is "twenty-one million, two hundred thirty-one thousand, five hundred forty".