21081685381 has 2 divisors, whose sum is σ = 21081685382. Its totient is φ = 21081685380.

The previous prime is 21081685351. The next prime is 21081685399. The reversal of 21081685381 is 18358618012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19441840356 + 1639845025 = 139434^2 + 40495^2 .

It is a cyclic number.

It is not a de Polignac number, because 21081685381 - 2¹¹ = 21081683333 is a prime.

It is a super-2 number, since 2×21081685381² (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 (21081685301) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10540842690 + 10540842691.

It is an arithmetic number, because the mean of its divisors is an integer number (10540842691).

Almost surely, 2^21081685381 is an apocalyptic number.

It is an amenable number.

21081685381 is a deficient number, since it is larger than the sum of its proper divisors (1).

21081685381 is an equidigital number, since it uses as much as digits as its factorization.

21081685381 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 92160, while the sum is 43.

The spelling of 21081685381 in words is "twenty-one billion, eighty-one million, six hundred eighty-five thousand, three hundred eighty-one".