215091661 has 4 divisors (see below), whose sum is σ = 215164512. Its totient is φ = 215018812.

The previous prime is 215091623. The next prime is 215091691. The reversal of 215091661 is 166190512.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-215091661 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (215091601) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 31801 + ... + 37966.

It is an arithmetic number, because the mean of its divisors is an integer number (53791128).

Almost surely, 2^215091661 is an apocalyptic number.

It is an amenable number.

215091661 is a deficient number, since it is larger than the sum of its proper divisors (72851).

215091661 is an equidigital number, since it uses as much as digits as its factorization.

215091661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 72850.

The product of its (nonzero) digits is 3240, while the sum is 31.

The square root of 215091661 is about 14666.0035797077. The cubic root of 215091661 is about 599.1577636535.

The spelling of 215091661 in words is "two hundred fifteen million, ninety-one thousand, six hundred sixty-one".