21129979957 has 2 divisors, whose sum is σ = 21129979958. Its totient is φ = 21129979956.

The previous prime is 21129979939. The next prime is 21129979973. The reversal of 21129979957 is 75997992112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18602504881 + 2527475076 = 136391^2 + 50274^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21129979957 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21129979895 and 21129979904.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21129979907) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10564989978 + 10564989979.

It is an arithmetic number, because the mean of its divisors is an integer number (10564989979).

Almost surely, 2^21129979957 is an apocalyptic number.

It is an amenable number.

21129979957 is a deficient number, since it is larger than the sum of its proper divisors (1).

21129979957 is an equidigital number, since it uses as much as digits as its factorization.

21129979957 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6429780, while the sum is 61.

The spelling of 21129979957 in words is "twenty-one billion, one hundred twenty-nine million, nine hundred seventy-nine thousand, nine hundred fifty-seven".