21643919634409 has 2 divisors, whose sum is σ = 21643919634410. Its totient is φ = 21643919634408.

The previous prime is 21643919634341. The next prime is 21643919634413. The reversal of 21643919634409 is 90443691934612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21275709753600 + 368209880809 = 4612560^2 + 606803^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21643919634409 is a prime.

It is not a weakly prime, because it can be changed into another prime (21643919634439) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10821959817204 + 10821959817205.

It is an arithmetic number, because the mean of its divisors is an integer number (10821959817205).

Almost surely, 2^{21643919634409} is an apocalyptic number.

It is an amenable number.

21643919634409 is a deficient number, since it is larger than the sum of its proper divisors (1).

21643919634409 is an equidigital number, since it uses as much as digits as its factorization.

21643919634409 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 30233088, while the sum is 61.

The spelling of 21643919634409 in words is "twenty-one trillion, six hundred forty-three billion, nine hundred nineteen million, six hundred thirty-four thousand, four hundred nine".