21661165208141 has 2 divisors, whose sum is σ = 21661165208142. Its totient is φ = 21661165208140.

The previous prime is 21661165208051. The next prime is 21661165208147. The reversal of 21661165208141 is 14180256116612.

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., 12159796668100 + 9501368540041 = 3487090^2 + 3082429^2 .

It is a cyclic number.

It is not a de Polignac number, because 21661165208141 - 2¹⁸ = 21661164945997 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21661165208092 and 21661165208101.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21661165208147) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10830582604070 + 10830582604071.

It is an arithmetic number, because the mean of its divisors is an integer number (10830582604071).

Almost surely, 2^{21661165208141} is an apocalyptic number.

It is an amenable number.

21661165208141 is a deficient number, since it is larger than the sum of its proper divisors (1).

21661165208141 is an equidigital number, since it uses as much as digits as its factorization.

21661165208141 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 138240, while the sum is 44.

The spelling of 21661165208141 in words is "twenty-one trillion, six hundred sixty-one billion, one hundred sixty-five million, two hundred eight thousand, one hundred forty-one".