21091953997 has 2 divisors, whose sum is σ = 21091953998. Its totient is φ = 21091953996.

The previous prime is 21091953977. The next prime is 21091954049. The reversal of 21091953997 is 79935919012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18844151076 + 2247802921 = 137274^2 + 47411^2 .

It is a cyclic number.

It is not a de Polignac number, because 21091953997 - 2²³ = 21083565389 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21091953977) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10545976998 + 10545976999.

It is an arithmetic number, because the mean of its divisors is an integer number (10545976999).

Almost surely, 2^21091953997 is an apocalyptic number.

It is an amenable number.

21091953997 is a deficient number, since it is larger than the sum of its proper divisors (1).

21091953997 is an equidigital number, since it uses as much as digits as its factorization.

21091953997 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1377810, while the sum is 55.

The spelling of 21091953997 in words is "twenty-one billion, ninety-one million, nine hundred fifty-three thousand, nine hundred ninety-seven".