28661221 has 2 divisors, whose sum is σ = 28661222. Its totient is φ = 28661220.

The previous prime is 28661219. The next prime is 28661257. The reversal of 28661221 is 12216682.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14516100 + 14145121 = 3810^2 + 3761^2 .

It is a cyclic number.

It is not a de Polignac number, because 28661221 - 2¹ = 28661219 is a prime.

Together with 28661219, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 28661221.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (28661021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 14330610 + 14330611.

It is an arithmetic number, because the mean of its divisors is an integer number (14330611).

Almost surely, 2^28661221 is an apocalyptic number.

It is an amenable number.

28661221 is a deficient number, since it is larger than the sum of its proper divisors (1).

28661221 is an equidigital number, since it uses as much as digits as its factorization.

28661221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2304, while the sum is 28.

The square root of 28661221 is about 5353.6175619855. The cubic root of 28661221 is about 306.0306297390.

It can be divided in two parts, 28661 and 221, that added together give a palindrome (28882).

The spelling of 28661221 in words is "twenty-eight million, six hundred sixty-one thousand, two hundred twenty-one".