21513423505421 has 2 divisors, whose sum is σ = 21513423505422. Its totient is φ = 21513423505420.

The previous prime is 21513423505391. The next prime is 21513423505433. The reversal of 21513423505421 is 12450532431512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12771052942921 + 8742370562500 = 3573661^2 + 2956750^2 .

It is a cyclic number.

It is not a de Polignac number, because 21513423505421 - 2²⁶ = 21513356396557 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21510423505421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10756711752710 + 10756711752711.

It is an arithmetic number, because the mean of its divisors is an integer number (10756711752711).

Almost surely, 2^{21513423505421} is an apocalyptic number.

It is an amenable number.

21513423505421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21513423505421 is an equidigital number, since it uses as much as digits as its factorization.

21513423505421 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 144000, while the sum is 38.

Adding to 21513423505421 its reverse (12450532431512), we get a palindrome (33963955936933).

The spelling of 21513423505421 in words is "twenty-one trillion, five hundred thirteen billion, four hundred twenty-three million, five hundred five thousand, four hundred twenty-one".