1866191221 has 2 divisors, whose sum is σ = 1866191222. Its totient is φ = 1866191220.

The previous prime is 1866191207. The next prime is 1866191251. The reversal of 1866191221 is 1221916681.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1631028996 + 235162225 = 40386^2 + 15335^2 .

It is a cyclic number.

It is not a de Polignac number, because 1866191221 - 2⁵ = 1866191189 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1866191251) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 933095610 + 933095611.

It is an arithmetic number, because the mean of its divisors is an integer number (933095611).

Almost surely, 2^1866191221 is an apocalyptic number.

It is an amenable number.

1866191221 is a deficient number, since it is larger than the sum of its proper divisors (1).

1866191221 is an equidigital number, since it uses as much as digits as its factorization.

1866191221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 10368, while the sum is 37.

The square root of 1866191221 is about 43199.4354245516. The cubic root of 1866191221 is about 1231.1719548012.

The spelling of 1866191221 in words is "one billion, eight hundred sixty-six million, one hundred ninety-one thousand, two hundred twenty-one".