21555072 has 256 divisors, whose sum is σ = 80294400. Its totient is φ = 5598720.

The previous prime is 21555067. The next prime is 21555097. The reversal of 21555072 is 27055512.

It is a happy number.

21555072 is a `hidden beast` number, since 2 + 155 + 507 + 2 = 666.

It is a super-2 number, since 2×21555072² = 929242257850368, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

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, 1959547 + ... + 1959557.

It is an arithmetic number, because the mean of its divisors is an integer number (313650).

Almost surely, 2^21555072 is an apocalyptic number.

21555072 is a gapful number since it is divisible by the number (22) 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 21555072, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40147200).

21555072 is an abundant number, since it is smaller than the sum of its proper divisors (58739328).

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

21555072 is an frugal number, since it uses more digits than its factorization.

21555072 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 53 (or 23 counting only the distinct ones).

The product of its (nonzero) digits is 3500, while the sum is 27.

The square root of 21555072 is about 4642.7440162042. The cubic root of 21555072 is about 278.3021058906.

It can be divided in two parts, 2155 and 5072, that added together give a palindrome (7227).

The spelling of 21555072 in words is "twenty-one million, five hundred fifty-five thousand, seventy-two".