21081617197 has 2 divisors, whose sum is σ = 21081617198. Its totient is φ = 21081617196.

The previous prime is 21081617171. The next prime is 21081617231. The reversal of 21081617197 is 79171618012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17896820841 + 3184796356 = 133779^2 + 56434^2 .

It is a cyclic number.

It is not a de Polignac number, because 21081617197 - 2¹⁵ = 21081584429 is a prime.

It is a super-2 number, since 2×21081617197² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21081617497) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10540808598 + 10540808599.

It is an arithmetic number, because the mean of its divisors is an integer number (10540808599).

Almost surely, 2^21081617197 is an apocalyptic number.

It is an amenable number.

21081617197 is a deficient number, since it is larger than the sum of its proper divisors (1).

21081617197 is an equidigital number, since it uses as much as digits as its factorization.

21081617197 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 42336, while the sum is 43.

The spelling of 21081617197 in words is "twenty-one billion, eighty-one million, six hundred seventeen thousand, one hundred ninety-seven".