21004042251817 has 2 divisors, whose sum is σ = 21004042251818. Its totient is φ = 21004042251816.

The previous prime is 21004042251811. The next prime is 21004042251833. The reversal of 21004042251817 is 71815224040012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21002275814976 + 1766436841 = 4582824^2 + 42029^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21004042251817 is a prime.

It is a super-2 number, since 2×21004042251817² (a number of 27 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21004042251811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10502021125908 + 10502021125909.

It is an arithmetic number, because the mean of its divisors is an integer number (10502021125909).

Almost surely, 2^{21004042251817} is an apocalyptic number.

It is an amenable number.

21004042251817 is a deficient number, since it is larger than the sum of its proper divisors (1).

21004042251817 is an equidigital number, since it uses as much as digits as its factorization.

21004042251817 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 35840, while the sum is 37.

Adding to 21004042251817 its reverse (71815224040012), we get a palindrome (92819266291829).

The spelling of 21004042251817 in words is "twenty-one trillion, four billion, forty-two million, two hundred fifty-one thousand, eight hundred seventeen".