21305781225 has 81 divisors (see below), whose sum is σ = 39369969093. Its totient is φ = 11013935040.

The previous prime is 21305781223. The next prime is 21305781227. The reversal of 21305781225 is 52218750312.

The square root of 21305781225 is 145965.

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

21305781225 is a `hidden beast` number, since 21 + 30 + 578 + 12 + 25 = 666.

It is an interprime number because it is at equal distance from previous prime (21305781223) and next prime (21305781227).

It can be written as a sum of positive squares in 4 ways, for example, as 2022570729 + 19283210496 = 44973^2 + 138864^2 .

It is not a de Polignac number, because 21305781225 - 2¹ = 21305781223 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21305781225.

It is not an unprimeable number, because it can be changed into a prime (21305781223) by changing a digit.

It is a polite number, since it can be written in 80 ways as a sum of consecutive naturals, for example, 81010444 + ... + 81010706.

Almost surely, 2^21305781225 is an apocalyptic number.

21305781225 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21305781225 is the 145965-th square number.

21305781225 is the 72983-rd centered octagonal number.

It is an amenable number.

21305781225 is a deficient number, since it is larger than the sum of its proper divisors (18064187868).

21305781225 is an equidigital number, since it uses as much as digits as its factorization.

21305781225 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 616 (or 308 counting only the distinct ones).

The product of its (nonzero) digits is 33600, while the sum is 36.

Multiplying 21305781225 by its sum of digits (36), we get a square (767008124100 = 875790²).

The spelling of 21305781225 in words is "twenty-one billion, three hundred five million, seven hundred eighty-one thousand, two hundred twenty-five".