21504360664637 has 2 divisors, whose sum is σ = 21504360664638. Its totient is φ = 21504360664636.

The previous prime is 21504360664603. The next prime is 21504360664673. The reversal of 21504360664637 is 73646606340512.

Together with next prime (21504360664673) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13963592030521 + 7540768634116 = 3736789^2 + 2746046^2 .

It is a cyclic number.

It is not a de Polignac number, because 21504360664637 - 2¹⁶ = 21504360599101 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21504360664337) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10752180332318 + 10752180332319.

It is an arithmetic number, because the mean of its divisors is an integer number (10752180332319).

Almost surely, 2^{21504360664637} is an apocalyptic number.

It is an amenable number.

21504360664637 is a deficient number, since it is larger than the sum of its proper divisors (1).

21504360664637 is an equidigital number, since it uses as much as digits as its factorization.

21504360664637 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 13063680, while the sum is 53.

The spelling of 21504360664637 in words is "twenty-one trillion, five hundred four billion, three hundred sixty million, six hundred sixty-four thousand, six hundred thirty-seven".