21517779901 has 2 divisors, whose sum is σ = 21517779902. Its totient is φ = 21517779900.

The previous prime is 21517779883. The next prime is 21517779917. The reversal of 21517779901 is 10997771512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18488928676 + 3028851225 = 135974^2 + 55035^2 .

It is a cyclic number.

It is not a de Polignac number, because 21517779901 - 2²⁷ = 21383562173 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21517779001) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10758889950 + 10758889951.

It is an arithmetic number, because the mean of its divisors is an integer number (10758889951).

Almost surely, 2^21517779901 is an apocalyptic number.

It is an amenable number.

21517779901 is a deficient number, since it is larger than the sum of its proper divisors (1).

21517779901 is an equidigital number, since it uses as much as digits as its factorization.

21517779901 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 277830, while the sum is 49.

The spelling of 21517779901 in words is "twenty-one billion, five hundred seventeen million, seven hundred seventy-nine thousand, nine hundred one".