21503440 has 160 divisors (see below), whose sum is σ = 62853120. Its totient is φ = 6676992.

The previous prime is 21503437. The next prime is 21503467. The reversal of 21503440 is 4430512.

It is a Harshad number since it is a multiple of its sum of digits (19).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 457497 + ... + 457543.

It is an arithmetic number, because the mean of its divisors is an integer number (392832).

Almost surely, 2^21503440 is an apocalyptic number.

21503440 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 21503440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31426560).

21503440 is an abundant number, since it is smaller than the sum of its proper divisors (41349680).

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

21503440 is a wasteful number, since it uses less digits than its factorization.

21503440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 129 (or 123 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 19.

The square root of 21503440 is about 4637.1801776511. The cubic root of 21503440 is about 278.0797176626.

21503440 divided by its sum of digits (19) gives a triangular number (1131760 = T₁₅₀₄).

Adding to 21503440 its reverse (4430512), we get a palindrome (25933952).

The spelling of 21503440 in words is "twenty-one million, five hundred three thousand, four hundred forty".