216421661 has 2 divisors, whose sum is σ = 216421662. Its totient is φ = 216421660.

The previous prime is 216421649. The next prime is 216421663. The reversal of 216421661 is 166124612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 169156036 + 47265625 = 13006^2 + 6875^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-216421661 is a prime.

Together with 216421663, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (216421663) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108210830 + 108210831.

It is an arithmetic number, because the mean of its divisors is an integer number (108210831).

Almost surely, 2^216421661 is an apocalyptic number.

It is an amenable number.

216421661 is a deficient number, since it is larger than the sum of its proper divisors (1).

216421661 is an equidigital number, since it uses as much as digits as its factorization.

216421661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3456, while the sum is 29.

The square root of 216421661 is about 14711.2766611195. The cubic root of 216421661 is about 600.3901730718.

The spelling of 216421661 in words is "two hundred sixteen million, four hundred twenty-one thousand, six hundred sixty-one".