213121665 has 32 divisors (see below), whose sum is σ = 389132160. Its totient is φ = 110590272.

The previous prime is 213121661. The next prime is 213121669. The reversal of 213121665 is 566121312.

It is an interprime number because it is at equal distance from previous prime (213121661) and next prime (213121669).

It is not a de Polignac number, because 213121665 - 2² = 213121661 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (213121661) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 16339 + ... + 26328.

It is an arithmetic number, because the mean of its divisors is an integer number (12160380).

Almost surely, 2^213121665 is an apocalyptic number.

It is an amenable number.

213121665 is a deficient number, since it is larger than the sum of its proper divisors (176010495).

213121665 is a wasteful number, since it uses less digits than its factorization.

213121665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42718 (or 42712 counting only the distinct ones).

The product of its digits is 2160, while the sum is 27.

The square root of 213121665 is about 14598.6870985031. The cubic root of 213121665 is about 597.3229484223.

Adding to 213121665 its reverse (566121312), we get a palindrome (779242977).

The spelling of 213121665 in words is "two hundred thirteen million, one hundred twenty-one thousand, six hundred sixty-five".