21990781861489 has 81 divisors (see below), whose sum is σ = 27457981375329. Its totient is φ = 17557237152000.

The previous prime is 21990781861481. The next prime is 21990781861501. The reversal of 21990781861489 is 98416818709912.

The square root of 21990781861489 is 4689433.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in 4 ways, for example, as 148057957089 + 21842723904400 = 384783^2 + 4673620^2 .

It is not a de Polignac number, because 21990781861489 - 2³ = 21990781861481 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21990781861481) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 80 ways as a sum of consecutive naturals, for example, 87612676614 + ... + 87612676864.

Almost surely, 2^{21990781861489} is an apocalyptic number.

21990781861489 is the 4689433-rd square number.

21990781861489 is the 2344717-th centered octagonal number.

It is an amenable number.

21990781861489 is a deficient number, since it is larger than the sum of its proper divisors (5467199513840).

21990781861489 is an frugal number, since it uses more digits than its factorization.

21990781861489 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 864 (or 432 counting only the distinct ones).

The product of its (nonzero) digits is 125411328, while the sum is 73.

The spelling of 21990781861489 in words is "twenty-one trillion, nine hundred ninety billion, seven hundred eighty-one million, eight hundred sixty-one thousand, four hundred eighty-nine".