1811621781225 has 81 divisors (see below), whose sum is σ = 3301125768837. Its totient is φ = 949712904000.

The previous prime is 1811621781133. The next prime is 1811621781239. The reversal of 1811621781225 is 5221871261181.

The square root of 1811621781225 is 1345965.

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

1811621781225 is a `hidden beast` number, since 1 + 8 + 1 + 1 + 621 + 7 + 8 + 12 + 2 + 5 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 834465807081 + 977155974144 = 913491^2 + 988512^2 .

It is not a de Polignac number, because 1811621781225 - 2⁷ = 1811621781097 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is an unprimeable number.

It is a polite number, since it can be written in 80 ways as a sum of consecutive naturals, for example, 1231557240 + ... + 1231558710.

Almost surely, 2^{1811621781225} is an apocalyptic number.

1811621781225 is a gapful number since it is divisible by the number (15) formed by its first and last digit.

1811621781225 is the 1345965-th square number.

1811621781225 is the 672983-rd centered octagonal number.

It is an amenable number.

1811621781225 is a deficient number, since it is larger than the sum of its proper divisors (1489503987612).

1811621781225 is an frugal number, since it uses more digits than its factorization.

1811621781225 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3080 (or 1540 counting only the distinct ones).

The product of its digits is 107520, while the sum is 45.

The spelling of 1811621781225 in words is "one trillion, eight hundred eleven billion, six hundred twenty-one million, seven hundred eighty-one thousand, two hundred twenty-five".