21756557197 has 2 divisors, whose sum is σ = 21756557198. Its totient is φ = 21756557196.

The previous prime is 21756557191. The next prime is 21756557203. The reversal of 21756557197 is 79175565712.

It is a balanced prime because it is at equal distance from previous prime (21756557191) and next prime (21756557203).

It can be written as a sum of positive squares in only one way, i.e., 21505049316 + 251507881 = 146646^2 + 15859^2 .

It is a cyclic number.

It is not a de Polignac number, because 21756557197 - 2¹⁵ = 21756524429 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21756557191) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10878278598 + 10878278599.

It is an arithmetic number, because the mean of its divisors is an integer number (10878278599).

Almost surely, 2^21756557197 is an apocalyptic number.

It is an amenable number.

21756557197 is a deficient number, since it is larger than the sum of its proper divisors (1).

21756557197 is an equidigital number, since it uses as much as digits as its factorization.

21756557197 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4630500, while the sum is 55.

The spelling of 21756557197 in words is "twenty-one billion, seven hundred fifty-six million, five hundred fifty-seven thousand, one hundred ninety-seven".