21256215004421 has 2 divisors, whose sum is σ = 21256215004422. Its totient is φ = 21256215004420.

The previous prime is 21256215004393. The next prime is 21256215004487. The reversal of 21256215004421 is 12440051265212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21239286132100 + 16928872321 = 4608610^2 + 130111^2 .

It is a cyclic number.

It is not a de Polignac number, because 21256215004421 - 2¹⁸ = 21256214742277 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21256215004121) 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, 10628107502210 + 10628107502211.

It is an arithmetic number, because the mean of its divisors is an integer number (10628107502211).

Almost surely, 2^{21256215004421} is an apocalyptic number.

It is an amenable number.

21256215004421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21256215004421 is an equidigital number, since it uses as much as digits as its factorization.

21256215004421 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 38400, while the sum is 35.

Adding to 21256215004421 its reverse (12440051265212), we get a palindrome (33696266269633).

The spelling of 21256215004421 in words is "twenty-one trillion, two hundred fifty-six billion, two hundred fifteen million, four thousand, four hundred twenty-one".