21000996509 has 2 divisors, whose sum is σ = 21000996510. Its totient is φ = 21000996508.

The previous prime is 21000996413. The next prime is 21000996557. The reversal of 21000996509 is 90569900012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15661771609 + 5339224900 = 125147^2 + 73070^2 .

It is a cyclic number.

It is not a de Polignac number, because 21000996509 - 2²⁰ = 20999947933 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21000996409) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500498254 + 10500498255.

It is an arithmetic number, because the mean of its divisors is an integer number (10500498255).

Almost surely, 2^21000996509 is an apocalyptic number.

It is an amenable number.

21000996509 is a deficient number, since it is larger than the sum of its proper divisors (1).

21000996509 is an equidigital number, since it uses as much as digits as its factorization.

21000996509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 43740, while the sum is 41.

The spelling of 21000996509 in words is "twenty-one billion, nine hundred ninety-six thousand, five hundred nine".