21720898 has 8 divisors (see below), whose sum is σ = 33376140. Its totient is φ = 10595520.

The previous prime is 21720877. The next prime is 21720899. The reversal of 21720898 is 89802712.

It can be written as a sum of positive squares in 2 ways, for example, as 17867529 + 3853369 = 4227^2 + 1963^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not an unprimeable number, because it can be changed into a prime (21720899) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 132363 + ... + 132526.

Almost surely, 2^21720898 is an apocalyptic number.

21720898 is a deficient number, since it is larger than the sum of its proper divisors (11655242).

21720898 is a wasteful number, since it uses less digits than its factorization.

21720898 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 264932.

The product of its (nonzero) digits is 16128, while the sum is 37.

The square root of 21720898 is about 4660.5684202681. The cubic root of 21720898 is about 279.0139551008.

It can be divided in two parts, 217 and 20898, that added together give a triangular number (21115 = T₂₀₅).

The spelling of 21720898 in words is "twenty-one million, seven hundred twenty thousand, eight hundred ninety-eight".