215123981 has 4 divisors (see below), whose sum is σ = 217341852. Its totient is φ = 212906112.

The previous prime is 215123959. The next prime is 215124011. The reversal of 215123981 is 189321512.

It is a happy number.

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

It can be written as a sum of positive squares in 2 ways, for example, as 66161956 + 148962025 = 8134^2 + 12205^2 .

It is a cyclic number.

It is not a de Polignac number, because 215123981 - 2⁶ = 215123917 is a prime.

It is a super-2 number, since 2×215123981² = 92556654402576722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (215123921) 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, 1108790 + ... + 1108983.

It is an arithmetic number, because the mean of its divisors is an integer number (54335463).

Almost surely, 2^215123981 is an apocalyptic number.

It is an amenable number.

215123981 is a deficient number, since it is larger than the sum of its proper divisors (2217871).

215123981 is an equidigital number, since it uses as much as digits as its factorization.

215123981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2217870.

The product of its digits is 4320, while the sum is 32.

The square root of 215123981 is about 14667.1054063165. The cubic root of 215123981 is about 599.1877722693.

The spelling of 215123981 in words is "two hundred fifteen million, one hundred twenty-three thousand, nine hundred eighty-one".