2197981986821 has 2 divisors, whose sum is σ = 2197981986822. Its totient is φ = 2197981986820.

The previous prime is 2197981986737. The next prime is 2197981986841. The reversal of 2197981986821 is 1286891897912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1128298581796 + 1069683405025 = 1062214^2 + 1034255^2 .

It is a cyclic number.

It is not a de Polignac number, because 2197981986821 - 2¹⁸ = 2197981724677 is a prime.

It is a super-2 number, since 2×2197981986821² (a number of 25 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (2197981986841) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1098990993410 + 1098990993411.

It is an arithmetic number, because the mean of its divisors is an integer number (1098990993411).

Almost surely, 2^{2197981986821} is an apocalyptic number.

It is an amenable number.

2197981986821 is a deficient number, since it is larger than the sum of its proper divisors (1).

2197981986821 is an equidigital number, since it uses as much as digits as its factorization.

2197981986821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 62705664, while the sum is 71.

The spelling of 2197981986821 in words is "two trillion, one hundred ninety-seven billion, nine hundred eighty-one million, nine hundred eighty-six thousand, eight hundred twenty-one".