21010278187809 has 9 divisors (see below), whose sum is σ = 30348199467313. Its totient is φ = 14006842957812.

The previous prime is 21010278187807. The next prime is 21010278187837. The reversal of 21010278187809 is 90878187201012.

The square root of 21010278187809 is 4583697.

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

21010278187809 is a `hidden beast` number, since 210 + 1 + 0 + 278 + 1 + 87 + 80 + 9 = 666.

It is a tau number, because it is divible by the number of its divisors (9).

It is not a de Polignac number, because 21010278187809 - 2¹ = 21010278187807 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21010278187807) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 12987142 + ... + 14515040.

Almost surely, 2^{21010278187809} is an apocalyptic number.

21010278187809 is the 4583697-th square number.

21010278187809 is the 2291849-th centered octagonal number.

It is an amenable number.

21010278187809 is a deficient number, since it is larger than the sum of its proper divisors (9337921279504).

21010278187809 is an frugal number, since it uses more digits than its factorization.

21010278187809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3055804 (or 1527902 counting only the distinct ones).

The product of its (nonzero) digits is 903168, while the sum is 54.

The spelling of 21010278187809 in words is "twenty-one trillion, ten billion, two hundred seventy-eight million, one hundred eighty-seven thousand, eight hundred nine".