19491221 has 2 divisors, whose sum is σ = 19491222. Its totient is φ = 19491220.

The previous prime is 19491217. The next prime is 19491223. The reversal of 19491221 is 12219491.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16200625 + 3290596 = 4025^2 + 1814^2 .

It is a cyclic number.

It is not a de Polignac number, because 19491221 - 2² = 19491217 is a prime.

It is a Sophie Germain prime.

Together with 19491223, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19491223) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9745610 + 9745611.

It is an arithmetic number, because the mean of its divisors is an integer number (9745611).

Almost surely, 2^19491221 is an apocalyptic number.

It is an amenable number.

19491221 is a deficient number, since it is larger than the sum of its proper divisors (1).

19491221 is an equidigital number, since it uses as much as digits as its factorization.

19491221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1296, while the sum is 29.

The square root of 19491221 is about 4414.8862952516. The cubic root of 19491221 is about 269.1202320425.

The spelling of 19491221 in words is "nineteen million, four hundred ninety-one thousand, two hundred twenty-one".