21555144 has 48 divisors (see below), whose sum is σ = 62871900. Its totient is φ = 6632064.

The previous prime is 21555113. The next prime is 21555179. The reversal of 21555144 is 44155512.

It can be written as a sum of positive squares in 2 ways, for example, as 21511044 + 44100 = 4638^2 + 210^2 .

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 10579 + ... + 12450.

Almost surely, 2^21555144 is an apocalyptic number.

21555144 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21555144 is an abundant number, since it is smaller than the sum of its proper divisors (41316756).

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

21555144 is a wasteful number, since it uses less digits than its factorization.

21555144 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23054 (or 23047 counting only the distinct ones).

The product of its digits is 4000, while the sum is 27.

The square root of 21555144 is about 4642.7517702328. The cubic root of 21555144 is about 278.3024157593.

The spelling of 21555144 in words is "twenty-one million, five hundred fifty-five thousand, one hundred forty-four".