221640661 has 6 divisors (see below), whose sum is σ = 243621686. Its totient is φ = 201491400.

The previous prime is 221640637. The next prime is 221640689. The reversal of 221640661 is 166046122.

It can be written as a sum of positive squares in only one way, i.e., 196700625 + 24940036 = 14025^2 + 4994^2 .

It is a de Polignac number, because none of the positive numbers 2^k-221640661 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (221643661) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 915750 + ... + 915991.

Almost surely, 2^221640661 is an apocalyptic number.

It is an amenable number.

221640661 is a deficient number, since it is larger than the sum of its proper divisors (21981025).

221640661 is a wasteful number, since it uses less digits than its factorization.

221640661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1831763 (or 1831752 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 28.

The square root of 221640661 is about 14887.6009148553. The cubic root of 221640661 is about 605.1780192386.

Adding to 221640661 its reverse (166046122), we get a palindrome (387686783).

The spelling of 221640661 in words is "two hundred twenty-one million, six hundred forty thousand, six hundred sixty-one".