21208728025 has 12 divisors (see below), whose sum is σ = 26300632252. Its totient is φ = 16965815040.

The previous prime is 21208727989. The next prime is 21208728071. The reversal of 21208728025 is 52082780212.

It is a happy number.

It can be written as a sum of positive squares in 6 ways, for example, as 926410969 + 20282317056 = 30437^2 + 142416^2 .

It is not a de Polignac number, because 21208728025 - 2⁹ = 21208727513 is a prime.

It is a hoax number, since the sum of its digits (37) coincides with the sum of the digits of its distinct prime factors.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 667909 + ... + 698941.

Almost surely, 2^21208728025 is an apocalyptic number.

21208728025 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21208728025 is a deficient number, since it is larger than the sum of its proper divisors (5091904227).

21208728025 is a wasteful number, since it uses less digits than its factorization.

21208728025 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 58380 (or 58375 counting only the distinct ones).

The product of its (nonzero) digits is 35840, while the sum is 37.

The spelling of 21208728025 in words is "twenty-one billion, two hundred eight million, seven hundred twenty-eight thousand, twenty-five".