221655661 has 2 divisors, whose sum is σ = 221655662. Its totient is φ = 221655660.

The previous prime is 221655659. The next prime is 221655683. The reversal of 221655661 is 166556122.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 160909225 + 60746436 = 12685^2 + 7794^2 .

It is a cyclic number.

It is not a de Polignac number, because 221655661 - 2¹ = 221655659 is a prime.

Together with 221655659, 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 (221655601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 110827830 + 110827831.

It is an arithmetic number, because the mean of its divisors is an integer number (110827831).

Almost surely, 2^221655661 is an apocalyptic number.

It is an amenable number.

221655661 is a deficient number, since it is larger than the sum of its proper divisors (1).

221655661 is an equidigital number, since it uses as much as digits as its factorization.

221655661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 21600, while the sum is 34.

The square root of 221655661 is about 14888.1046812548. The cubic root of 221655661 is about 605.1916711643.

The spelling of 221655661 in words is "two hundred twenty-one million, six hundred fifty-five thousand, six hundred sixty-one".