21518267761 has 2 divisors, whose sum is σ = 21518267762. Its totient is φ = 21518267760.

The previous prime is 21518267747. The next prime is 21518267767. The reversal of 21518267761 is 16776281512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20586797361 + 931470400 = 143481^2 + 30520^2 .

It is a cyclic number.

It is not a de Polignac number, because 21518267761 - 2²⁵ = 21484713329 is a prime.

It is not a weakly prime, because it can be changed into another prime (21518267767) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10759133880 + 10759133881.

It is an arithmetic number, because the mean of its divisors is an integer number (10759133881).

Almost surely, 2^21518267761 is an apocalyptic number.

It is an amenable number.

21518267761 is a deficient number, since it is larger than the sum of its proper divisors (1).

21518267761 is an equidigital number, since it uses as much as digits as its factorization.

21518267761 is an evil number, because the sum of its binary digits is even.

The product of its digits is 282240, while the sum is 46.

The spelling of 21518267761 in words is "twenty-one billion, five hundred eighteen million, two hundred sixty-seven thousand, seven hundred sixty-one".