21156673121 has 2 divisors, whose sum is σ = 21156673122. Its totient is φ = 21156673120.

The previous prime is 21156673117. The next prime is 21156673133. The reversal of 21156673121 is 12137665112.

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., 18147053521 + 3009619600 = 134711^2 + 54860^2 .

It is a cyclic number.

It is not a de Polignac number, because 21156673121 - 2² = 21156673117 is a prime.

It is not a weakly prime, because it can be changed into another prime (21156673721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10578336560 + 10578336561.

It is an arithmetic number, because the mean of its divisors is an integer number (10578336561).

Almost surely, 2^21156673121 is an apocalyptic number.

It is an amenable number.

21156673121 is a deficient number, since it is larger than the sum of its proper divisors (1).

21156673121 is an equidigital number, since it uses as much as digits as its factorization.

21156673121 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15120, while the sum is 35.

The spelling of 21156673121 in words is "twenty-one billion, one hundred fifty-six million, six hundred seventy-three thousand, one hundred twenty-one".