21017544221 has 2 divisors, whose sum is σ = 21017544222. Its totient is φ = 21017544220.

The previous prime is 21017544169. The next prime is 21017544253. The reversal of 21017544221 is 12244571012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20899039225 + 118504996 = 144565^2 + 10886^2 .

It is a cyclic number.

It is not a de Polignac number, because 21017544221 - 2⁶ = 21017544157 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21017544281) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10508772110 + 10508772111.

It is an arithmetic number, because the mean of its divisors is an integer number (10508772111).

Almost surely, 2^21017544221 is an apocalyptic number.

It is an amenable number.

21017544221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21017544221 is an equidigital number, since it uses as much as digits as its factorization.

21017544221 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 4480, while the sum is 29.

The spelling of 21017544221 in words is "twenty-one billion, seventeen million, five hundred forty-four thousand, two hundred twenty-one".