1221115611681 has 81 divisors (see below), whose sum is σ = 2076307778649. Its totient is φ = 689545584000.

The previous prime is 1221115611647. The next prime is 1221115611707. The reversal of 1221115611681 is 1861165111221.

It is a happy number.

The square root of 1221115611681 is 1105041.

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

1221115611681 is a `hidden beast` number, since 1 + 2 + 2 + 1 + 1 + 1 + 561 + 16 + 81 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 156215448081 + 1064900163600 = 395241^2 + 1031940^2 .

It is not a de Polignac number, because 1221115611681 - 2¹¹ = 1221115609633 is a prime.

It is a super-2 number, since 2×1221115611681² (a number of 25 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (1221115611631) 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, 2343791701 + ... + 2343792221.

Almost surely, 2^{1221115611681} is an apocalyptic number.

1221115611681 is the 1105041-st square number.

1221115611681 is the 552521-st centered octagonal number.

It is an amenable number.

1221115611681 is a deficient number, since it is larger than the sum of its proper divisors (855192166968).

1221115611681 is an frugal number, since it uses more digits than its factorization.

1221115611681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1264 (or 632 counting only the distinct ones).

The product of its digits is 5760, while the sum is 36.

Multiplying 1221115611681 by its sum of digits (36), we get a square (43960162020516 = 6630246²).

The spelling of 1221115611681 in words is "one trillion, two hundred twenty-one billion, one hundred fifteen million, six hundred eleven thousand, six hundred eighty-one".