216991551 has 36 divisors (see below), whose sum is σ = 342463752. Its totient is φ = 121855104.

The previous prime is 216991547. The next prime is 216991559. The reversal of 216991551 is 155199612.

It is not a de Polignac number, because 216991551 - 2² = 216991547 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (216991559) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 783225 + ... + 783501.

It is an arithmetic number, because the mean of its divisors is an integer number (9512882).

Almost surely, 2^216991551 is an apocalyptic number.

216991551 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

216991551 is a deficient number, since it is larger than the sum of its proper divisors (125472201).

216991551 is an equidigital number, since it uses as much as digits as its factorization.

216991551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 440 (or 360 counting only the distinct ones).

The product of its digits is 24300, while the sum is 39.

The square root of 216991551 is about 14730.6330821184. The cubic root of 216991551 is about 600.9167014951.

The spelling of 216991551 in words is "two hundred sixteen million, nine hundred ninety-one thousand, five hundred fifty-one".