21166551979 has 2 divisors, whose sum is σ = 21166551980. Its totient is φ = 21166551978.

The previous prime is 21166551881. The next prime is 21166552009. The reversal of 21166551979 is 97915566112.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21166551979 - 2¹¹ = 21166549931 is a prime.

It is not a weakly prime, because it can be changed into another prime (21166551179) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10583275989 + 10583275990.

It is an arithmetic number, because the mean of its divisors is an integer number (10583275990).

Almost surely, 2^21166551979 is an apocalyptic number.

21166551979 is a deficient number, since it is larger than the sum of its proper divisors (1).

21166551979 is an equidigital number, since it uses as much as digits as its factorization.

21166551979 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1020600, while the sum is 52.

The spelling of 21166551979 in words is "twenty-one billion, one hundred sixty-six million, five hundred fifty-one thousand, nine hundred seventy-nine".