21642551162509 has 2 divisors, whose sum is σ = 21642551162510. Its totient is φ = 21642551162508.

The previous prime is 21642551162473. The next prime is 21642551162513. The reversal of 21642551162509 is 90526115524612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15671384864100 + 5971166298409 = 3958710^2 + 2443597^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21642551162509 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21642551162809) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10821275581254 + 10821275581255.

It is an arithmetic number, because the mean of its divisors is an integer number (10821275581255).

Almost surely, 2^{21642551162509} is an apocalyptic number.

It is an amenable number.

21642551162509 is a deficient number, since it is larger than the sum of its proper divisors (1).

21642551162509 is an equidigital number, since it uses as much as digits as its factorization.

21642551162509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1296000, while the sum is 49.

The spelling of 21642551162509 in words is "twenty-one trillion, six hundred forty-two billion, five hundred fifty-one million, one hundred sixty-two thousand, five hundred nine".