21318215609 has 2 divisors, whose sum is σ = 21318215610. Its totient is φ = 21318215608.

The previous prime is 21318215539. The next prime is 21318215617. The reversal of 21318215609 is 90651281312.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13893808384 + 7424407225 = 117872^2 + 86165^2 .

It is a cyclic number.

It is not a de Polignac number, because 21318215609 - 2²⁰ = 21317167033 is a prime.

It is a super-2 number, since 2×21318215609² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21318215629) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10659107804 + 10659107805.

It is an arithmetic number, because the mean of its divisors is an integer number (10659107805).

Almost surely, 2^21318215609 is an apocalyptic number.

It is an amenable number.

21318215609 is a deficient number, since it is larger than the sum of its proper divisors (1).

21318215609 is an equidigital number, since it uses as much as digits as its factorization.

21318215609 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 25920, while the sum is 38.

The spelling of 21318215609 in words is "twenty-one billion, three hundred eighteen million, two hundred fifteen thousand, six hundred nine".