21621540 has 48 divisors (see below), whose sum is σ = 60919488. Its totient is φ = 5729664.

The previous prime is 21621527. The next prime is 21621547. The reversal of 21621540 is 4512612.

It is not an unprimeable number, because it can be changed into a prime (21621547) 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, 9339 + ... + 11421.

It is an arithmetic number, because the mean of its divisors is an integer number (1269156).

Almost surely, 2^21621540 is an apocalyptic number.

21621540 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21621540 is an abundant number, since it is smaller than the sum of its proper divisors (39297948).

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

21621540 is a wasteful number, since it uses less digits than its factorization.

21621540 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2268 (or 2266 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 21.

The square root of 21621540 is about 4649.8967730478. The cubic root of 21621540 is about 278.5878731722.

The spelling of 21621540 in words is "twenty-one million, six hundred twenty-one thousand, five hundred forty".