21517306477561 has 2 divisors, whose sum is σ = 21517306477562. Its totient is φ = 21517306477560.

The previous prime is 21517306477559. The next prime is 21517306477619. The reversal of 21517306477561 is 16577460371512.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21389468765625 + 127837711936 = 4624875^2 + 357544^2 .

It is a cyclic number.

It is not a de Polignac number, because 21517306477561 - 2¹ = 21517306477559 is a prime.

Together with 21517306477559, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21517336477561) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10758653238780 + 10758653238781.

It is an arithmetic number, because the mean of its divisors is an integer number (10758653238781).

Almost surely, 2^{21517306477561} is an apocalyptic number.

It is an amenable number.

21517306477561 is a deficient number, since it is larger than the sum of its proper divisors (1).

21517306477561 is an equidigital number, since it uses as much as digits as its factorization.

21517306477561 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 7408800, while the sum is 55.

The spelling of 21517306477561 in words is "twenty-one trillion, five hundred seventeen billion, three hundred six million, four hundred seventy-seven thousand, five hundred sixty-one".