21455123021 has 2 divisors, whose sum is σ = 21455123022. Its totient is φ = 21455123020.

The previous prime is 21455122999. The next prime is 21455123023. The reversal of 21455123021 is 12032155412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18658194025 + 2796928996 = 136595^2 + 52886^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21455123021 is a prime.

Together with 21455123023, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21455123023) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10727561510 + 10727561511.

It is an arithmetic number, because the mean of its divisors is an integer number (10727561511).

Almost surely, 2^21455123021 is an apocalyptic number.

It is an amenable number.

21455123021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21455123021 is an equidigital number, since it uses as much as digits as its factorization.

21455123021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2400, while the sum is 26.

Adding to 21455123021 its reverse (12032155412), we get a palindrome (33487278433).

The spelling of 21455123021 in words is "twenty-one billion, four hundred fifty-five million, one hundred twenty-three thousand, twenty-one".