216508381 has 2 divisors, whose sum is σ = 216508382. Its totient is φ = 216508380.

The previous prime is 216508307. The next prime is 216508417. The reversal of 216508381 is 183805612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 151044100 + 65464281 = 12290^2 + 8091^2 .

It is a cyclic number.

It is not a de Polignac number, because 216508381 - 2²¹ = 214411229 is a prime.

It is a super-2 number, since 2×216508381² = 93751758086482322, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (216508081) 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 as a sum of consecutive naturals, namely, 108254190 + 108254191.

It is an arithmetic number, because the mean of its divisors is an integer number (108254191).

Almost surely, 2^216508381 is an apocalyptic number.

It is an amenable number.

216508381 is a deficient number, since it is larger than the sum of its proper divisors (1).

216508381 is an equidigital number, since it uses as much as digits as its factorization.

216508381 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 11520, while the sum is 34.

The square root of 216508381 is about 14714.2237647794. The cubic root of 216508381 is about 600.4703543298.

The spelling of 216508381 in words is "two hundred sixteen million, five hundred eight thousand, three hundred eighty-one".