21005309453 has 2 divisors, whose sum is σ = 21005309454. Its totient is φ = 21005309452.

The previous prime is 21005309443. The next prime is 21005309473. The reversal of 21005309453 is 35490350012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19027995364 + 1977314089 = 137942^2 + 44467^2 .

It is a cyclic number.

It is not a de Polignac number, because 21005309453 - 2⁶ = 21005309389 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21005309443) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10502654726 + 10502654727.

It is an arithmetic number, because the mean of its divisors is an integer number (10502654727).

Almost surely, 2^21005309453 is an apocalyptic number.

It is an amenable number.

21005309453 is a deficient number, since it is larger than the sum of its proper divisors (1).

21005309453 is an equidigital number, since it uses as much as digits as its factorization.

21005309453 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 16200, while the sum is 32.

Adding to 21005309453 its reverse (35490350012), we get a palindrome (56495659465).

The spelling of 21005309453 in words is "twenty-one billion, five million, three hundred nine thousand, four hundred fifty-three".