21506212165597 has 2 divisors, whose sum is σ = 21506212165598. Its totient is φ = 21506212165596.

The previous prime is 21506212165591. The next prime is 21506212165621. The reversal of 21506212165597 is 79556121260512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20981658169476 + 524553996121 = 4580574^2 + 724261^2 .

It is a cyclic number.

It is not a de Polignac number, because 21506212165597 - 2³ = 21506212165589 is a prime.

It is a super-3 number, since 3×21506212165597³ (a number of 41 digits) contains 333 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21506212165591) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10753106082798 + 10753106082799.

It is an arithmetic number, because the mean of its divisors is an integer number (10753106082799).

Almost surely, 2^{21506212165597} is an apocalyptic number.

It is an amenable number.

21506212165597 is a deficient number, since it is larger than the sum of its proper divisors (1).

21506212165597 is an equidigital number, since it uses as much as digits as its factorization.

21506212165597 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2268000, while the sum is 52.

The spelling of 21506212165597 in words is "twenty-one trillion, five hundred six billion, two hundred twelve million, one hundred sixty-five thousand, five hundred ninety-seven".