216499781 has 2 divisors, whose sum is σ = 216499782. Its totient is φ = 216499780.

The previous prime is 216499769. The next prime is 216499807. The reversal of 216499781 is 187994612.

216499781 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 172396900 + 44102881 = 13130^2 + 6641^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-216499781 is a prime.

It is a super-2 number, since 2×216499781² = 93744310346095922, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (216498781) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108249890 + 108249891.

It is an arithmetic number, because the mean of its divisors is an integer number (108249891).

Almost surely, 2^216499781 is an apocalyptic number.

It is an amenable number.

216499781 is a deficient number, since it is larger than the sum of its proper divisors (1).

216499781 is an equidigital number, since it uses as much as digits as its factorization.

216499781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 217728, while the sum is 47.

The square root of 216499781 is about 14713.9315276373. The cubic root of 216499781 is about 600.4624037316.

The spelling of 216499781 in words is "two hundred sixteen million, four hundred ninety-nine thousand, seven hundred eighty-one".