216523400021 has 2 divisors, whose sum is σ = 216523400022. Its totient is φ = 216523400020.

The previous prime is 216523400003. The next prime is 216523400053. The reversal of 216523400021 is 120004325612.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 140134179025 + 76389220996 = 374345^2 + 276386^2 .

It is a cyclic number.

It is not a de Polignac number, because 216523400021 - 2¹⁰ = 216523398997 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (216523400521) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108261700010 + 108261700011.

It is an arithmetic number, because the mean of its divisors is an integer number (108261700011).

Almost surely, 2^216523400021 is an apocalyptic number.

It is an amenable number.

216523400021 is a deficient number, since it is larger than the sum of its proper divisors (1).

216523400021 is an equidigital number, since it uses as much as digits as its factorization.

216523400021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2880, while the sum is 26.

Adding to 216523400021 its reverse (120004325612), we get a palindrome (336527725633).

The spelling of 216523400021 in words is "two hundred sixteen billion, five hundred twenty-three million, four hundred thousand, twenty-one".