21208611517 has 2 divisors, whose sum is σ = 21208611518. Its totient is φ = 21208611516.

The previous prime is 21208611497. The next prime is 21208611563. The reversal of 21208611517 is 71511680212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19549352761 + 1659258756 = 139819^2 + 40734^2 .

It is a cyclic number.

It is not a de Polignac number, because 21208611517 - 2²⁷ = 21074393789 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21208612517) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10604305758 + 10604305759.

It is an arithmetic number, because the mean of its divisors is an integer number (10604305759).

Almost surely, 2^21208611517 is an apocalyptic number.

It is an amenable number.

21208611517 is a deficient number, since it is larger than the sum of its proper divisors (1).

21208611517 is an equidigital number, since it uses as much as digits as its factorization.

21208611517 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6720, while the sum is 34.

The spelling of 21208611517 in words is "twenty-one billion, two hundred eight million, six hundred eleven thousand, five hundred seventeen".