21129988 has 36 divisors (see below), whose sum is σ = 41057100. Its totient is φ = 9507520.

The previous prime is 21129961. The next prime is 21129989. The reversal of 21129988 is 88992112.

It can be written as a sum of positive squares in 2 ways, for example, as 11778624 + 9351364 = 3432^2 + 3058^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21129988.

It is not an unprimeable number, because it can be changed into a prime (21129989) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 71970 + ... + 72262.

It is an arithmetic number, because the mean of its divisors is an integer number (1140475).

Almost surely, 2^21129988 is an apocalyptic number.

It is an amenable number.

21129988 is a deficient number, since it is larger than the sum of its proper divisors (19927112).

21129988 is a wasteful number, since it uses less digits than its factorization.

21129988 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 468 (or 455 counting only the distinct ones).

The product of its digits is 20736, while the sum is 40.

The square root of 21129988 is about 4596.7366685509. The cubic root of 21129988 is about 276.4604963909.

It can be divided in two parts, 2112 and 9988, that added together give a square (12100 = 110²).

The spelling of 21129988 in words is "twenty-one million, one hundred twenty-nine thousand, nine hundred eighty-eight".