21187781225 has 12 divisors (see below), whose sum is σ = 28293837516. Its totient is φ = 15646361280.

The previous prime is 21187781213. The next prime is 21187781261. The reversal of 21187781225 is 52218778112.

It can be written as a sum of positive squares in 6 ways, for example, as 975187984 + 20212593241 = 31228^2 + 142171^2 .

It is not a de Polignac number, because 21187781225 - 2²⁰ = 21186732649 is a prime.

It is a hoax number, since the sum of its digits (44) 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, 32596262 + ... + 32596911.

It is an arithmetic number, because the mean of its divisors is an integer number (2357819793).

Almost surely, 2^21187781225 is an apocalyptic number.

21187781225 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21187781225 is a deficient number, since it is larger than the sum of its proper divisors (7106056291).

21187781225 is a wasteful number, since it uses less digits than its factorization.

21187781225 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 65193196 (or 65193191 counting only the distinct ones).

The product of its digits is 125440, while the sum is 44.

The spelling of 21187781225 in words is "twenty-one billion, one hundred eighty-seven million, seven hundred eighty-one thousand, two hundred twenty-five".