217097991 has 48 divisors (see below), whose sum is σ = 356548608. Its totient is φ = 126100800.

The previous prime is 217097987. The next prime is 217097999. The reversal of 217097991 is 199790712.

217097991 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 217097991 - 2² = 217097987 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (217097999) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 389485 + ... + 390041.

It is an arithmetic number, because the mean of its divisors is an integer number (7428096).

Almost surely, 2^217097991 is an apocalyptic number.

217097991 is a deficient number, since it is larger than the sum of its proper divisors (139450617).

217097991 is a wasteful number, since it uses less digits than its factorization.

217097991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 732 (or 729 counting only the distinct ones).

The product of its (nonzero) digits is 71442, while the sum is 45.

The square root of 217097991 is about 14734.2455185191. The cubic root of 217097991 is about 601.0149405248.

The spelling of 217097991 in words is "two hundred seventeen million, ninety-seven thousand, nine hundred ninety-one".