21663614521 has 2 divisors, whose sum is σ = 21663614522. Its totient is φ = 21663614520.

The previous prime is 21663614477. The next prime is 21663614537. The reversal of 21663614521 is 12541636612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19053937296 + 2609677225 = 138036^2 + 51085^2 .

It is a cyclic number.

It is not a de Polignac number, because 21663614521 - 2²³ = 21655225913 is a prime.

It is a super-2 number, since 2×21663614521² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21663614221) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10831807260 + 10831807261.

It is an arithmetic number, because the mean of its divisors is an integer number (10831807261).

Almost surely, 2^21663614521 is an apocalyptic number.

It is an amenable number.

21663614521 is a deficient number, since it is larger than the sum of its proper divisors (1).

21663614521 is an equidigital number, since it uses as much as digits as its factorization.

21663614521 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 51840, while the sum is 37.

The spelling of 21663614521 in words is "twenty-one billion, six hundred sixty-three million, six hundred fourteen thousand, five hundred twenty-one".