21565163281 has 2 divisors, whose sum is σ = 21565163282. Its totient is φ = 21565163280.

The previous prime is 21565163209. The next prime is 21565163327. The reversal of 21565163281 is 18236156512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20921018881 + 644144400 = 144641^2 + 25380^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21565163281 is a prime.

It is a super-2 number, since 2×21565163281² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21565193281) 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, 10782581640 + 10782581641.

It is an arithmetic number, because the mean of its divisors is an integer number (10782581641).

Almost surely, 2^21565163281 is an apocalyptic number.

It is an amenable number.

21565163281 is a deficient number, since it is larger than the sum of its proper divisors (1).

21565163281 is an equidigital number, since it uses as much as digits as its factorization.

21565163281 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 86400, while the sum is 40.

The spelling of 21565163281 in words is "twenty-one billion, five hundred sixty-five million, one hundred sixty-three thousand, two hundred eighty-one".