217978 has 8 divisors (see below), whose sum is σ = 331668. Its totient is φ = 107424.

The previous prime is 217969. The next prime is 217979. The reversal of 217978 is 879712.

It can be written as a sum of positive squares in 2 ways, for example, as 205209 + 12769 = 453^2 + 113^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a plaindrome in base 15.

It is not an unprimeable number, because it can be changed into a prime (217979) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 601 + ... + 892.

2²¹⁷⁹⁷⁸ is an apocalyptic number.

217978 is a deficient number, since it is larger than the sum of its proper divisors (113690).

217978 is a wasteful number, since it uses less digits than its factorization.

217978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1568.

The product of its digits is 7056, while the sum is 34.

The square root of 217978 is about 466.8811411912. The cubic root of 217978 is about 60.1825919210.

It can be divided in two parts, 217 and 978, that multiplied together give a triangular number (212226 = T₆₅₁).

The spelling of 217978 in words is "two hundred seventeen thousand, nine hundred seventy-eight".