21171956779 has 2 divisors, whose sum is σ = 21171956780. Its totient is φ = 21171956778.

The previous prime is 21171956759. The next prime is 21171956801. The reversal of 21171956779 is 97765917112.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21171956779 - 2¹¹ = 21171954731 is a prime.

It is not a weakly prime, because it can be changed into another prime (21171956759) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10585978389 + 10585978390.

It is an arithmetic number, because the mean of its divisors is an integer number (10585978390).

Almost surely, 2^21171956779 is an apocalyptic number.

21171956779 is a deficient number, since it is larger than the sum of its proper divisors (1).

21171956779 is an equidigital number, since it uses as much as digits as its factorization.

21171956779 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1666980, while the sum is 55.

The spelling of 21171956779 in words is "twenty-one billion, one hundred seventy-one million, nine hundred fifty-six thousand, seven hundred seventy-nine".