21356145991 has 2 divisors, whose sum is σ = 21356145992. Its totient is φ = 21356145990.

The previous prime is 21356145989. The next prime is 21356146067. The reversal of 21356145991 is 19954165312.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21356145991 - 2¹ = 21356145989 is a prime.

Together with 21356145989, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21356145191) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10678072995 + 10678072996.

It is an arithmetic number, because the mean of its divisors is an integer number (10678072996).

Almost surely, 2^21356145991 is an apocalyptic number.

21356145991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21356145991 is an equidigital number, since it uses as much as digits as its factorization.

21356145991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 291600, while the sum is 46.

The spelling of 21356145991 in words is "twenty-one billion, three hundred fifty-six million, one hundred forty-five thousand, nine hundred ninety-one".