21738221 has 2 divisors, whose sum is σ = 21738222. Its totient is φ = 21738220.

The previous prime is 21738191. The next prime is 21738239. The reversal of 21738221 is 12283712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17682025 + 4056196 = 4205^2 + 2014^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21738221 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21738251) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10869110 + 10869111.

It is an arithmetic number, because the mean of its divisors is an integer number (10869111).

Almost surely, 2^21738221 is an apocalyptic number.

It is an amenable number.

21738221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21738221 is an equidigital number, since it uses as much as digits as its factorization.

21738221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1344, while the sum is 26.

The square root of 21738221 is about 4662.4265141662. The cubic root of 21738221 is about 279.0881091006.

The spelling of 21738221 in words is "twenty-one million, seven hundred thirty-eight thousand, two hundred twenty-one".