21661457343821 has 2 divisors, whose sum is σ = 21661457343822. Its totient is φ = 21661457343820.

The previous prime is 21661457343749. The next prime is 21661457343881. The reversal of 21661457343821 is 12834375416612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19617272281321 + 2044185062500 = 4429139^2 + 1429750^2 .

It is a cyclic number.

It is not a de Polignac number, because 21661457343821 - 2²² = 21661453149517 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21661457343881) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10830728671910 + 10830728671911.

It is an arithmetic number, because the mean of its divisors is an integer number (10830728671911).

Almost surely, 2^{21661457343821} is an apocalyptic number.

It is an amenable number.

21661457343821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21661457343821 is an equidigital number, since it uses as much as digits as its factorization.

21661457343821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5806080, while the sum is 53.

The spelling of 21661457343821 in words is "twenty-one trillion, six hundred sixty-one billion, four hundred fifty-seven million, three hundred forty-three thousand, eight hundred twenty-one".