217947981 has 4 divisors (see below), whose sum is σ = 290597312. Its totient is φ = 145298652.

The previous prime is 217947941. The next prime is 217947991. The reversal of 217947981 is 189749712.

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 not a de Polignac number, because 217947981 - 2⁷ = 217947853 is a prime.

It is a super-3 number, since 3×217947981³ (a number of 26 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 217947981.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (217947901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 36324661 + ... + 36324666.

It is an arithmetic number, because the mean of its divisors is an integer number (72649328).

Almost surely, 2^217947981 is an apocalyptic number.

It is an amenable number.

217947981 is a deficient number, since it is larger than the sum of its proper divisors (72649331).

217947981 is an equidigital number, since it uses as much as digits as its factorization.

217947981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 72649330.

The product of its digits is 254016, while the sum is 48.

The square root of 217947981 is about 14763.0613695128. The cubic root of 217947981 is about 601.7982909758.

The spelling of 217947981 in words is "two hundred seventeen million, nine hundred forty-seven thousand, nine hundred eighty-one".