21100347878681 has 2 divisors, whose sum is σ = 21100347878682. Its totient is φ = 21100347878680.

The previous prime is 21100347878647. The next prime is 21100347878683. The reversal of 21100347878681 is 18687874300112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12281134758025 + 8819213120656 = 3504445^2 + 2969716^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21100347878681 is a prime.

It is a super-2 number, since 2×21100347878681² (a number of 27 digits) contains 22 as substring.

Together with 21100347878683, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21100347878683) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10550173939340 + 10550173939341.

It is an arithmetic number, because the mean of its divisors is an integer number (10550173939341).

Almost surely, 2^{21100347878681} is an apocalyptic number.

It is an amenable number.

21100347878681 is a deficient number, since it is larger than the sum of its proper divisors (1).

21100347878681 is an equidigital number, since it uses as much as digits as its factorization.

21100347878681 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3612672, while the sum is 56.

The spelling of 21100347878681 in words is "twenty-one trillion, one hundred billion, three hundred forty-seven million, eight hundred seventy-eight thousand, six hundred eighty-one".