216021997 has 2 divisors, whose sum is σ = 216021998. Its totient is φ = 216021996.

The previous prime is 216021983. The next prime is 216022031. The reversal of 216021997 is 799120612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 145226601 + 70795396 = 12051^2 + 8414^2 .

It is a cyclic number.

It is not a de Polignac number, because 216021997 - 2¹⁵ = 215989229 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (216027997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108010998 + 108010999.

It is an arithmetic number, because the mean of its divisors is an integer number (108010999).

Almost surely, 2^216021997 is an apocalyptic number.

It is an amenable number.

216021997 is a deficient number, since it is larger than the sum of its proper divisors (1).

216021997 is an equidigital number, since it uses as much as digits as its factorization.

216021997 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 13608, while the sum is 37.

The square root of 216021997 is about 14697.6867907845. The cubic root of 216021997 is about 600.0203669012.

The spelling of 216021997 in words is "two hundred sixteen million, twenty-one thousand, nine hundred ninety-seven".