21071566156721 has 2 divisors, whose sum is σ = 21071566156722. Its totient is φ = 21071566156720.

The previous prime is 21071566156691. The next prime is 21071566156759. The reversal of 21071566156721 is 12765166517012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13306627230625 + 7764938926096 = 3647825^2 + 2786564^2 .

It is a cyclic number.

It is not a de Polignac number, because 21071566156721 - 2³⁴ = 21054386287537 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21071566156721.

It is not a weakly prime, because it can be changed into another prime (21071566156321) 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, 10535783078360 + 10535783078361.

It is an arithmetic number, because the mean of its divisors is an integer number (10535783078361).

Almost surely, 2^{21071566156721} is an apocalyptic number.

It is an amenable number.

21071566156721 is a deficient number, since it is larger than the sum of its proper divisors (1).

21071566156721 is an equidigital number, since it uses as much as digits as its factorization.

21071566156721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1058400, while the sum is 50.

The spelling of 21071566156721 in words is "twenty-one trillion, seventy-one billion, five hundred sixty-six million, one hundred fifty-six thousand, seven hundred twenty-one".