21361742681 has 2 divisors, whose sum is σ = 21361742682. Its totient is φ = 21361742680.

The previous prime is 21361742657. The next prime is 21361742687. The reversal of 21361742681 is 18624716312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21182182681 + 179560000 = 145541^2 + 13400^2 .

It is a cyclic number.

It is not a de Polignac number, because 21361742681 - 2¹⁸ = 21361480537 is a prime.

It is a super-2 number, since 2×21361742681² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21361742687) 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, 10680871340 + 10680871341.

It is an arithmetic number, because the mean of its divisors is an integer number (10680871341).

Almost surely, 2^21361742681 is an apocalyptic number.

It is an amenable number.

21361742681 is a deficient number, since it is larger than the sum of its proper divisors (1).

21361742681 is an equidigital number, since it uses as much as digits as its factorization.

21361742681 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 96768, while the sum is 41.

The spelling of 21361742681 in words is "twenty-one billion, three hundred sixty-one million, seven hundred forty-two thousand, six hundred eighty-one".