216662561 has 2 divisors, whose sum is σ = 216662562. Its totient is φ = 216662560.

The previous prime is 216662557. The next prime is 216662581. The reversal of 216662561 is 165266612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 195132961 + 21529600 = 13969^2 + 4640^2 .

It is a cyclic number.

It is not a de Polignac number, because 216662561 - 2² = 216662557 is a prime.

It is not a weakly prime, because it can be changed into another prime (216662581) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108331280 + 108331281.

It is an arithmetic number, because the mean of its divisors is an integer number (108331281).

Almost surely, 2^216662561 is an apocalyptic number.

It is an amenable number.

216662561 is a deficient number, since it is larger than the sum of its proper divisors (1).

216662561 is an equidigital number, since it uses as much as digits as its factorization.

216662561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 25920, while the sum is 35.

The square root of 216662561 is about 14719.4619806568. The cubic root of 216662561 is about 600.6128562064.

The spelling of 216662561 in words is "two hundred sixteen million, six hundred sixty-two thousand, five hundred sixty-one".