21215526817 has 2 divisors, whose sum is σ = 21215526818. Its totient is φ = 21215526816.

The previous prime is 21215526809. The next prime is 21215526847. The reversal of 21215526817 is 71862551212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21150175761 + 65351056 = 145431^2 + 8084^2 .

It is a cyclic number.

It is not a de Polignac number, because 21215526817 - 2³ = 21215526809 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21215526817.

It is not a weakly prime, because it can be changed into another prime (21215526847) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10607763408 + 10607763409.

It is an arithmetic number, because the mean of its divisors is an integer number (10607763409).

Almost surely, 2^21215526817 is an apocalyptic number.

It is an amenable number.

21215526817 is a deficient number, since it is larger than the sum of its proper divisors (1).

21215526817 is an equidigital number, since it uses as much as digits as its factorization.

21215526817 is an evil number, because the sum of its binary digits is even.

The product of its digits is 67200, while the sum is 40.

The spelling of 21215526817 in words is "twenty-one billion, two hundred fifteen million, five hundred twenty-six thousand, eight hundred seventeen".