21508017258997 has 2 divisors, whose sum is σ = 21508017258998. Its totient is φ = 21508017258996.

The previous prime is 21508017258947. The next prime is 21508017259033. The reversal of 21508017258997 is 79985271080512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20701853905041 + 806163353956 = 4549929^2 + 897866^2 .

It is a cyclic number.

It is not a de Polignac number, because 21508017258997 - 2¹⁵ = 21508017226229 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21508017258907) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10754008629498 + 10754008629499.

It is an arithmetic number, because the mean of its divisors is an integer number (10754008629499).

Almost surely, 2^{21508017258997} is an apocalyptic number.

It is an amenable number.

21508017258997 is a deficient number, since it is larger than the sum of its proper divisors (1).

21508017258997 is an equidigital number, since it uses as much as digits as its factorization.

21508017258997 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 25401600, while the sum is 64.

The spelling of 21508017258997 in words is "twenty-one trillion, five hundred eight billion, seventeen million, two hundred fifty-eight thousand, nine hundred ninety-seven".