21256043016391 has 2 divisors, whose sum is σ = 21256043016392. Its totient is φ = 21256043016390.

The previous prime is 21256043016371. The next prime is 21256043016409. The reversal of 21256043016391 is 19361034065212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21256043016391 - 2⁴¹ = 19057019760839 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21256043016311) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10628021508195 + 10628021508196.

It is an arithmetic number, because the mean of its divisors is an integer number (10628021508196).

Almost surely, 2^{21256043016391} is an apocalyptic number.

21256043016391 is a deficient number, since it is larger than the sum of its proper divisors (1).

21256043016391 is an equidigital number, since it uses as much as digits as its factorization.

21256043016391 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 233280, while the sum is 43.

The spelling of 21256043016391 in words is "twenty-one trillion, two hundred fifty-six billion, forty-three million, sixteen thousand, three hundred ninety-one".