21209553225 has 243 divisors, whose sum is σ = 47286791253. Its totient is φ = 9059662080.

The previous prime is 21209553223. The next prime is 21209553283. The reversal of 21209553225 is 52235590212.

The square root of 21209553225 is 145635.

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

21209553225 is a `hidden beast` number, since 2 + 12 + 0 + 95 + 532 + 25 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 116057529 + 21093495696 = 10773^2 + 145236^2 .

It is not a de Polignac number, because 21209553225 - 2¹ = 21209553223 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21209553225.

It is not an unprimeable number, because it can be changed into a prime (21209553223) 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 242 ways as a sum of consecutive naturals, for example, 290541789 + ... + 290541861.

Almost surely, 2^21209553225 is an apocalyptic number.

21209553225 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21209553225 is the 145635-th square number.

21209553225 is the 72818-th centered octagonal number.

It is an amenable number.

21209553225 is an abundant number, since it is smaller than the sum of its proper divisors (26077238028).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21209553225 is a wasteful number, since it uses less digits than its factorization.

21209553225 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 214 (or 107 counting only the distinct ones).

The product of its (nonzero) digits is 54000, while the sum is 36.

Multiplying 21209553225 by its sum of digits (36), we get a square (763543916100 = 873810²).

The spelling of 21209553225 in words is "twenty-one billion, two hundred nine million, five hundred fifty-three thousand, two hundred twenty-five".