21981490 has 16 divisors (see below), whose sum is σ = 39620952. Its totient is φ = 8780544.

The previous prime is 21981469. The next prime is 21981497. The reversal of 21981490 is 9418912.

It can be written as a sum of positive squares in 4 ways, for example, as 19722481 + 2259009 = 4441^2 + 1503^2 .

It is not an unprimeable number, because it can be changed into a prime (21981497) 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 7 ways as a sum of consecutive naturals, for example, 11482 + ... + 13258.

Almost surely, 2^21981490 is an apocalyptic number.

21981490 is a deficient number, since it is larger than the sum of its proper divisors (17639462).

21981490 is a wasteful number, since it uses less digits than its factorization.

21981490 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3021.

The product of its (nonzero) digits is 5184, while the sum is 34.

The square root of 21981490 is about 4688.4421719799. The cubic root of 21981490 is about 280.1253265492.

Subtracting from 21981490 its reverse (9418912), we obtain a triangular number (12562578 = T₅₀₁₂).

The spelling of 21981490 in words is "twenty-one million, nine hundred eighty-one thousand, four hundred ninety".