21125750409 has 9 divisors (see below), whose sum is σ = 30515602663. Its totient is φ = 14083542912.

The previous prime is 21125750363. The next prime is 21125750423. The reversal of 21125750409 is 90405752112.

The square root of 21125750409 is 145347.

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

21125750409 is a `hidden beast` number, since 21 + 125 + 7 + 504 + 0 + 9 = 666.

It can be written as a sum of positive squares in only one way, i.e., 21040372809 + 85377600 = 145053^2 + 9240^2 .

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

It is not a de Polignac number, because 21125750409 - 2¹⁹ = 21125226121 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21125750509) 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, 411817 + ... + 460265.

Almost surely, 2^21125750409 is an apocalyptic number.

21125750409 is the 145347-th square number.

21125750409 is the 72674-th centered octagonal number.

It is an amenable number.

21125750409 is a deficient number, since it is larger than the sum of its proper divisors (9389852254).

21125750409 is an frugal number, since it uses more digits than its factorization.

21125750409 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 96904 (or 48452 counting only the distinct ones).

The product of its (nonzero) digits is 25200, while the sum is 36.

Multiplying 21125750409 by its sum of digits (36), we get a square (760527014724 = 872082²).

The spelling of 21125750409 in words is "twenty-one billion, one hundred twenty-five million, seven hundred fifty thousand, four hundred nine".