21661165732447 has 2 divisors, whose sum is σ = 21661165732448. Its totient is φ = 21661165732446.

The previous prime is 21661165732429. The next prime is 21661165732471. The reversal of 21661165732447 is 74423756116612.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21661165732447 is a prime.

It is a super-2 number, since 2×21661165732447² (a number of 27 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21661165732847) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10830582866223 + 10830582866224.

It is an arithmetic number, because the mean of its divisors is an integer number (10830582866224).

Almost surely, 2^{21661165732447} is an apocalyptic number.

21661165732447 is a deficient number, since it is larger than the sum of its proper divisors (1).

21661165732447 is an equidigital number, since it uses as much as digits as its factorization.

21661165732447 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 10160640, while the sum is 55.

The spelling of 21661165732447 in words is "twenty-one trillion, six hundred sixty-one billion, one hundred sixty-five million, seven hundred thirty-two thousand, four hundred forty-seven".