221220261665 has 64 divisors (see below), whose sum is σ = 299146478400. Its totient is φ = 155921117184.

The previous prime is 221220261641. The next prime is 221220261697. The reversal of 221220261665 is 566162022122.

It can be written as a sum of positive squares in 32 ways, for example, as 173542229056 + 47678032609 = 416584^2 + 218353^2 .

It is a cyclic number.

It is not a de Polignac number, because 221220261665 - 2¹⁸ = 221219999521 is a prime.

It is a super-2 number, since 2×221220261665² (a number of 23 digits) contains 22 as substring.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 114443039 + ... + 114444971.

It is an arithmetic number, because the mean of its divisors is an integer number (4674163725).

Almost surely, 2^221220261665 is an apocalyptic number.

It is an amenable number.

221220261665 is a deficient number, since it is larger than the sum of its proper divisors (77926216735).

221220261665 is a wasteful number, since it uses less digits than its factorization.

221220261665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2646.

The product of its (nonzero) digits is 34560, while the sum is 35.

Adding to 221220261665 its reverse (566162022122), we get a palindrome (787382283787).

The spelling of 221220261665 in words is "two hundred twenty-one billion, two hundred twenty million, two hundred sixty-one thousand, six hundred sixty-five".