66261797818225 has 27 divisors (see below), whose sum is σ = 84902216962881. Its totient is φ = 51298479559200.

The previous prime is 66261797818211. The next prime is 66261797818243. The reversal of 66261797818225 is 52281879716266.

The square root of 66261797818225 is 8140135.

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

It can be written as a sum of positive squares in 4 ways, for example, as 2662193614129 + 63599604204096 = 1631623^2 + 7974936^2 .

It is not a de Polignac number, because 66261797818225 - 2¹⁵ = 66261797785457 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 1261694667 + ... + 1261747183.

Almost surely, 2^{66261797818225} is an apocalyptic number.

66261797818225 is the 8140135-th square number.

66261797818225 is the 4070068-th centered octagonal number.

It is an amenable number.

66261797818225 is a deficient number, since it is larger than the sum of its proper divisors (18640419144656).

66261797818225 is an frugal number, since it uses more digits than its factorization.

66261797818225 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 105106 (or 52553 counting only the distinct ones).

The product of its digits is 243855360, while the sum is 70.

The spelling of 66261797818225 in words is "sixty-six trillion, two hundred sixty-one billion, seven hundred ninety-seven million, eight hundred eighteen thousand, two hundred twenty-five".