21221020217 has 2 divisors, whose sum is σ = 21221020218. Its totient is φ = 21221020216.

The previous prime is 21221020201. The next prime is 21221020229. The reversal of 21221020217 is 71202012212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12039356176 + 9181664041 = 109724^2 + 95821^2 .

It is a cyclic number.

It is not a de Polignac number, because 21221020217 - 2⁴ = 21221020201 is a prime.

It is not a weakly prime, because it can be changed into another prime (21221020237) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10610510108 + 10610510109.

It is an arithmetic number, because the mean of its divisors is an integer number (10610510109).

Almost surely, 2^21221020217 is an apocalyptic number.

It is an amenable number.

21221020217 is a deficient number, since it is larger than the sum of its proper divisors (1).

21221020217 is an equidigital number, since it uses as much as digits as its factorization.

21221020217 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 224, while the sum is 20.

Adding to 21221020217 its reverse (71202012212), we get a palindrome (92423032429).

The spelling of 21221020217 in words is "twenty-one billion, two hundred twenty-one million, twenty thousand, two hundred seventeen".