215810991 has 12 divisors (see below), whose sum is σ = 340065960. Its totient is φ = 130794480.

The previous prime is 215810951. The next prime is 215810993. The reversal of 215810991 is 199018512.

It is not a de Polignac number, because 215810991 - 2⁹ = 215810479 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (215810993) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1089856 + ... + 1090053.

It is an arithmetic number, because the mean of its divisors is an integer number (28338830).

Almost surely, 2^215810991 is an apocalyptic number.

215810991 is a deficient number, since it is larger than the sum of its proper divisors (124254969).

215810991 is a wasteful number, since it uses less digits than its factorization.

215810991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2179926 (or 2179923 counting only the distinct ones).

The product of its (nonzero) digits is 6480, while the sum is 36.

The square root of 215810991 is about 14690.5068326454. The cubic root of 215810991 is about 599.8249405953.

The spelling of 215810991 in words is "two hundred fifteen million, eight hundred ten thousand, nine hundred ninety-one".