21000021221 has 2 divisors, whose sum is σ = 21000021222. Its totient is φ = 21000021220.

The previous prime is 21000021197. The next prime is 21000021283. The reversal of 21000021221 is 12212000012.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20694261025 + 305760196 = 143855^2 + 17486^2 .

It is a cyclic number.

It is not a de Polignac number, because 21000021221 - 2³⁰ = 19926279397 is a prime.

It is a super-4 number, since 4×21000021221⁴ (a number of 42 digits) contains 4444 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21000021421) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500010610 + 10500010611.

It is an arithmetic number, because the mean of its divisors is an integer number (10500010611).

Almost surely, 2^21000021221 is an apocalyptic number.

It is an amenable number.

21000021221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21000021221 is an equidigital number, since it uses as much as digits as its factorization.

21000021221 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 16, while the sum is 11.

Adding to 21000021221 its reverse (12212000012), we get a palindrome (33212021233).

The spelling of 21000021221 in words is "twenty-one billion, twenty-one thousand, two hundred twenty-one".