215781 has 8 divisors (see below), whose sum is σ = 304704. Its totient is φ = 135360.

The previous prime is 215771. The next prime is 215797. The reversal of 215781 is 187512.

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

It is not a de Polignac number, because 215781 - 2⁷ = 215653 is a prime.

It is a super-2 number, since 2×215781² = 93122879922, which contains 22 as substring.

It is a plaindrome in base 14.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (215771) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2065 + ... + 2166.

It is an arithmetic number, because the mean of its divisors is an integer number (38088).

2²¹⁵⁷⁸¹ is an apocalyptic number.

It is an amenable number.

215781 is a deficient number, since it is larger than the sum of its proper divisors (88923).

215781 is a wasteful number, since it uses less digits than its factorization.

215781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4251.

The product of its digits is 560, while the sum is 24.

The square root of 215781 is about 464.5223353080. The cubic root of 215781 is about 59.9797153652.

The spelling of 215781 in words is "two hundred fifteen thousand, seven hundred eighty-one".