21020221997 has 2 divisors, whose sum is σ = 21020221998. Its totient is φ = 21020221996.

The previous prime is 21020221907. The next prime is 21020222029. The reversal of 21020221997 is 79912202012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14082331561 + 6937890436 = 118669^2 + 83294^2 .

It is a cyclic number.

It is not a de Polignac number, because 21020221997 - 2¹⁸ = 21019959853 is a prime.

It is a super-3 number, since 3×21020221997³ (a number of 32 digits) contains 333 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21020221907) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10510110998 + 10510110999.

It is an arithmetic number, because the mean of its divisors is an integer number (10510110999).

Almost surely, 2^21020221997 is an apocalyptic number.

It is an amenable number.

21020221997 is a deficient number, since it is larger than the sum of its proper divisors (1).

21020221997 is an equidigital number, since it uses as much as digits as its factorization.

21020221997 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 9072, while the sum is 35.

The spelling of 21020221997 in words is "twenty-one billion, twenty million, two hundred twenty-one thousand, nine hundred ninety-seven".