21249540 has 120 divisors (see below), whose sum is σ = 71859480. Its totient is φ = 5225472.

The previous prime is 21249523. The next prime is 21249559. The reversal of 21249540 is 4594212.

It can be written as a sum of positive squares in 4 ways, for example, as 15876 + 21233664 = 126^2 + 4608^2 .

It is a Harshad number since it is a multiple of its sum of digits (27).

It is an unprimeable number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 20556 + ... + 21564.

It is an arithmetic number, because the mean of its divisors is an integer number (598829).

Almost surely, 2^21249540 is an apocalyptic number.

21249540 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 21249540, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35929740).

21249540 is an abundant number, since it is smaller than the sum of its proper divisors (50609940).

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

21249540 is a wasteful number, since it uses less digits than its factorization.

21249540 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1043 (or 1032 counting only the distinct ones).

The product of its (nonzero) digits is 2880, while the sum is 27.

The square root of 21249540 is about 4609.7223343711. The cubic root of 21249540 is about 276.9809142015.

It can be divided in two parts, 2124 and 9540, that added together give a square (11664 = 108²).

The spelling of 21249540 in words is "twenty-one million, two hundred forty-nine thousand, five hundred forty".