21281788 has 48 divisors (see below), whose sum is σ = 42674688. Its totient is φ = 9200000.

The previous prime is 21281783. The next prime is 21281797. The reversal of 21281788 is 88718212.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21281783) 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, 84663 + ... + 84913.

It is an arithmetic number, because the mean of its divisors is an integer number (889056).

Almost surely, 2^21281788 is an apocalyptic number.

It is an amenable number.

21281788 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

21281788 is a wasteful number, since it uses less digits than its factorization.

21281788 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 354 (or 352 counting only the distinct ones).

The product of its digits is 14336, while the sum is 37.

The square root of 21281788 is about 4613.2188328758. The cubic root of 21281788 is about 277.1209574829.

It can be divided in two parts, 2128 and 1788, that added together give a triangular number (3916 = T₈₈).

The spelling of 21281788 in words is "twenty-one million, two hundred eighty-one thousand, seven hundred eighty-eight".