663699961 has 4 divisors (see below), whose sum is σ = 663754612. Its totient is φ = 663645312.

The previous prime is 663699943. The next prime is 663699991. The reversal of 663699961 is 169996366.

It is a happy number.

663699961 is a nontrivial binomial coefficient, being equal to C(36434, 2).

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 169996366 = 2 ⋅84998183.

It can be written as a sum of positive squares in 2 ways, for example, as 381459961 + 282240000 = 19531^2 + 16800^2 .

It is a 3-Lehmer number, since φ(663699961) divides (663699961-1)³.

It is a cyclic number.

It is not a de Polignac number, because 663699961 - 2⁷ = 663699833 is a prime.

It is not an unprimeable number, because it can be changed into a prime (663699991) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1 + ... + 36433.

It is an arithmetic number, because the mean of its divisors is an integer number (165938653).

It is a Poulet number, since it divides 2^663699960-1.

Almost surely, 2^663699961 is an apocalyptic number.

663699961 is the 36433-rd triangular number and also the 18217-th hexagonal number.

663699961 is the 12145-th centered nonagonal number.

It is an amenable number.

663699961 is a deficient number, since it is larger than the sum of its proper divisors (54651).

663699961 is a wasteful number, since it uses less digits than its factorization.

663699961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 54650.

The product of its digits is 2834352, while the sum is 55.

The square root of 663699961 is about 25762.3749099341. The cubic root of 663699961 is about 872.2827097423.

The spelling of 663699961 in words is "six hundred sixty-three million, six hundred ninety-nine thousand, nine hundred sixty-one".