216351661 has 2 divisors, whose sum is σ = 216351662. Its totient is φ = 216351660.

The previous prime is 216351659. The next prime is 216351713. The reversal of 216351661 is 166153612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 215208900 + 1142761 = 14670^2 + 1069^2 .

It is a cyclic number.

It is not a de Polignac number, because 216351661 - 2¹ = 216351659 is a prime.

Together with 216351659, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (216358661) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108175830 + 108175831.

It is an arithmetic number, because the mean of its divisors is an integer number (108175831).

Almost surely, 2^216351661 is an apocalyptic number.

It is an amenable number.

216351661 is a deficient number, since it is larger than the sum of its proper divisors (1).

216351661 is an equidigital number, since it uses as much as digits as its factorization.

216351661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6480, while the sum is 31.

The square root of 216351661 is about 14708.8973414053. The cubic root of 216351661 is about 600.3254354914.

It can be divided in two parts, 2163 and 51661, that added together give a square (53824 = 232²).

The spelling of 216351661 in words is "two hundred sixteen million, three hundred fifty-one thousand, six hundred sixty-one".