21021019709 has 2 divisors, whose sum is σ = 21021019710. Its totient is φ = 21021019708.

The previous prime is 21021019667. The next prime is 21021019711. The reversal of 21021019709 is 90791012012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14456455225 + 6564564484 = 120235^2 + 81022^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21021019709 is a prime.

Together with 21021019711, 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 (21021019729) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10510509854 + 10510509855.

It is an arithmetic number, because the mean of its divisors is an integer number (10510509855).

Almost surely, 2^21021019709 is an apocalyptic number.

It is an amenable number.

21021019709 is a deficient number, since it is larger than the sum of its proper divisors (1).

21021019709 is an equidigital number, since it uses as much as digits as its factorization.

21021019709 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2268, while the sum is 32.

The spelling of 21021019709 in words is "twenty-one billion, twenty-one million, nineteen thousand, seven hundred nine".