215971681 has 4 divisors (see below), whose sum is σ = 216209664. Its totient is φ = 215733700.

The previous prime is 215971669. The next prime is 215971697. The reversal of 215971681 is 186179512.

It is a happy number.

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 a cyclic number.

It is not a de Polignac number, because 215971681 - 2⁵ = 215971649 is a prime.

It is a super-2 number, since 2×215971681² = 93287533987931522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (215971181) 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, 117625 + ... + 119446.

It is an arithmetic number, because the mean of its divisors is an integer number (54052416).

Almost surely, 2^215971681 is an apocalyptic number.

It is an amenable number.

215971681 is a deficient number, since it is larger than the sum of its proper divisors (237983).

215971681 is an equidigital number, since it uses as much as digits as its factorization.

215971681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 237982.

The product of its digits is 30240, while the sum is 40.

The square root of 215971681 is about 14695.9749931742. The cubic root of 215971681 is about 599.9737775577.

The spelling of 215971681 in words is "two hundred fifteen million, nine hundred seventy-one thousand, six hundred eighty-one".