216021491 has 4 divisors (see below), whose sum is σ = 246881712. Its totient is φ = 185161272.

The previous prime is 216021473. The next prime is 216021511. The reversal of 216021491 is 194120612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 216021491 - 2⁶ = 216021427 is a prime.

It is a zygodrome in base 2.

It is a self number, because there is not a number n which added to its sum of digits gives 216021491.

It is not an unprimeable number, because it can be changed into a prime (216021461) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 15430100 + ... + 15430113.

It is an arithmetic number, because the mean of its divisors is an integer number (61720428).

Almost surely, 2^216021491 is an apocalyptic number.

216021491 is a deficient number, since it is larger than the sum of its proper divisors (30860221).

216021491 is an equidigital number, since it uses as much as digits as its factorization.

216021491 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 30860220.

The product of its (nonzero) digits is 864, while the sum is 26.

The square root of 216021491 is about 14697.6695771813. The cubic root of 216021491 is about 600.0198984142.

The spelling of 216021491 in words is "two hundred sixteen million, twenty-one thousand, four hundred ninety-one".