21655240 has 16 divisors (see below), whose sum is σ = 48724380. Its totient is φ = 8662080.

The previous prime is 21655223. The next prime is 21655247. The reversal of 21655240 is 4255612.

It can be written as a sum of positive squares in 2 ways, for example, as 20052484 + 1602756 = 4478^2 + 1266^2 .

It is not an unprimeable number, because it can be changed into a prime (21655247) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 270651 + ... + 270730.

Almost surely, 2^21655240 is an apocalyptic number.

21655240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21655240 is an abundant number, since it is smaller than the sum of its proper divisors (27069140).

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

21655240 is a wasteful number, since it uses less digits than its factorization.

21655240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 541392 (or 541388 counting only the distinct ones).

The product of its (nonzero) digits is 2400, while the sum is 25.

The square root of 21655240 is about 4653.5190984888. The cubic root of 21655240 is about 278.7325365936.

The spelling of 21655240 in words is "twenty-one million, six hundred fifty-five thousand, two hundred forty".