21003540 has 48 divisors (see below), whose sum is σ = 60842880. Its totient is φ = 5407360.

The previous prime is 21003539. The next prime is 21003547. The reversal of 21003540 is 4530012.

It is a super-2 number, since 2×21003540² = 882297385063200, which contains 22 as substring.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21003547) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4296 + ... + 7775.

It is an arithmetic number, because the mean of its divisors is an integer number (1267560).

Almost surely, 2^21003540 is an apocalyptic number.

21003540 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21003540 is an abundant number, since it is smaller than the sum of its proper divisors (39839340).

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

21003540 is a wasteful number, since it uses less digits than its factorization.

21003540 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12112 (or 12110 counting only the distinct ones).

The product of its (nonzero) digits is 120, while the sum is 15.

The square root of 21003540 is about 4582.9619243454. The cubic root of 21003540 is about 275.9079192934.

Adding to 21003540 its reverse (4530012), we get a palindrome (25533552).

The spelling of 21003540 in words is "twenty-one million, three thousand, five hundred forty".