21012320621 has 2 divisors, whose sum is σ = 21012320622. Its totient is φ = 21012320620.

The previous prime is 21012320551. The next prime is 21012320677. The reversal of 21012320621 is 12602321012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12752055625 + 8260264996 = 112925^2 + 90886^2 .

It is a cyclic number.

It is not a de Polignac number, because 21012320621 - 2¹⁰ = 21012319597 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21012320593 and 21012320602.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21012350621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10506160310 + 10506160311.

It is an arithmetic number, because the mean of its divisors is an integer number (10506160311).

Almost surely, 2^21012320621 is an apocalyptic number.

It is an amenable number.

21012320621 is a deficient number, since it is larger than the sum of its proper divisors (1).

21012320621 is an equidigital number, since it uses as much as digits as its factorization.

21012320621 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 288, while the sum is 20.

Adding to 21012320621 its reverse (12602321012), we get a palindrome (33614641633).

The spelling of 21012320621 in words is "twenty-one billion, twelve million, three hundred twenty thousand, six hundred twenty-one".