21503640 has 128 divisors (see below), whose sum is σ = 69672960. Its totient is φ = 5289984.

The previous prime is 21503621. The next prime is 21503653. The reversal of 21503640 is 4630512.

It is a happy number.

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, 169257 + ... + 169383.

It is an arithmetic number, because the mean of its divisors is an integer number (544320).

Almost surely, 2^21503640 is an apocalyptic number.

21503640 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 21503640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34836480).

21503640 is an abundant number, since it is smaller than the sum of its proper divisors (48169320).

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

21503640 is a wasteful number, since it uses less digits than its factorization.

21503640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 241 (or 237 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 21.

The square root of 21503640 is about 4637.2017424304. The cubic root of 21503640 is about 278.0805797846.

The spelling of 21503640 in words is "twenty-one million, five hundred three thousand, six hundred forty".