21723238781 has 2 divisors, whose sum is σ = 21723238782. Its totient is φ = 21723238780.

The previous prime is 21723238777. The next prime is 21723238807. The reversal of 21723238781 is 18783232712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19524472900 + 2198765881 = 139730^2 + 46891^2 .

It is a cyclic number.

It is not a de Polignac number, because 21723238781 - 2² = 21723238777 is a prime.

It is a super-2 number, since 2×21723238781² (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 (21723238751) 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, 10861619390 + 10861619391.

It is an arithmetic number, because the mean of its divisors is an integer number (10861619391).

Almost surely, 2^21723238781 is an apocalyptic number.

It is an amenable number.

21723238781 is a deficient number, since it is larger than the sum of its proper divisors (1).

21723238781 is an equidigital number, since it uses as much as digits as its factorization.

21723238781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 225792, while the sum is 44.

The spelling of 21723238781 in words is "twenty-one billion, seven hundred twenty-three million, two hundred thirty-eight thousand, seven hundred eighty-one".