21173878181 has 2 divisors, whose sum is σ = 21173878182. Its totient is φ = 21173878180.

The previous prime is 21173878151. The next prime is 21173878241. The reversal of 21173878181 is 18187837112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15137365156 + 6036513025 = 123034^2 + 77695^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21173878181 is a prime.

It is a super-2 number, since 2×21173878181² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21173878111) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10586939090 + 10586939091.

It is an arithmetic number, because the mean of its divisors is an integer number (10586939091).

Almost surely, 2^21173878181 is an apocalyptic number.

It is an amenable number.

21173878181 is a deficient number, since it is larger than the sum of its proper divisors (1).

21173878181 is an equidigital number, since it uses as much as digits as its factorization.

21173878181 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 150528, while the sum is 47.

The spelling of 21173878181 in words is "twenty-one billion, one hundred seventy-three million, eight hundred seventy-eight thousand, one hundred eighty-one".