1663905681 has 9 divisors (see below), whose sum is σ = 2403596091. Its totient is φ = 1109188872.

The previous prime is 1663905679. The next prime is 1663905707. The reversal of 1663905681 is 1865093661.

The square root of 1663905681 is 40791.

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

1663905681 is a `hidden beast` number, since 1 + 6 + 639 + 0 + 5 + 6 + 8 + 1 = 666.

1663905681 is digitally balanced in base 4, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in only one way, i.e., 149450625 + 1514455056 = 12225^2 + 38916^2 .

It is a tau number, because it is divible by the number of its divisors (9).

It is not a de Polignac number, because 1663905681 - 2¹ = 1663905679 is a prime.

It is a super-2 number, since 2×1663905681² = 5537164230528147522, which contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (1663905611) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 115575 + ... + 129171.

Almost surely, 2^1663905681 is an apocalyptic number.

1663905681 is the 40791-st square number.

1663905681 is the 20396-th centered octagonal number.

It is an amenable number.

1663905681 is a deficient number, since it is larger than the sum of its proper divisors (739690410).

1663905681 is an frugal number, since it uses more digits than its factorization.

1663905681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27200 (or 13600 counting only the distinct ones).

The product of its (nonzero) digits is 233280, while the sum is 45.

The cubic root of 1663905681 is about 1184.9760375435.

The spelling of 1663905681 in words is "one billion, six hundred sixty-three million, nine hundred five thousand, six hundred eighty-one".