21110021221 has 2 divisors, whose sum is σ = 21110021222. Its totient is φ = 21110021220.

The previous prime is 21110021173. The next prime is 21110021239. The reversal of 21110021221 is 12212001112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19533137121 + 1576884100 = 139761^2 + 39710^2 .

It is a cyclic number.

It is not a de Polignac number, because 21110021221 - 2¹⁵ = 21109988453 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21110021321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10555010610 + 10555010611.

It is an arithmetic number, because the mean of its divisors is an integer number (10555010611).

Almost surely, 2^21110021221 is an apocalyptic number.

It is an amenable number.

21110021221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21110021221 is an equidigital number, since it uses as much as digits as its factorization.

21110021221 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 16, while the sum is 13.

Adding to 21110021221 its reverse (12212001112), we get a palindrome (33322022333).

The spelling of 21110021221 in words is "twenty-one billion, one hundred ten million, twenty-one thousand, two hundred twenty-one".