211220021981 has 2 divisors, whose sum is σ = 211220021982. Its totient is φ = 211220021980.

The previous prime is 211220021963. The next prime is 211220022011. The reversal of 211220021981 is 189120022112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 188004624025 + 23215397956 = 433595^2 + 152366^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-211220021981 is a prime.

It is a super-2 number, since 2×211220021981² (a number of 23 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (211220021911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 105610010990 + 105610010991.

It is an arithmetic number, because the mean of its divisors is an integer number (105610010991).

Almost surely, 2^211220021981 is an apocalyptic number.

It is an amenable number.

211220021981 is a deficient number, since it is larger than the sum of its proper divisors (1).

211220021981 is an equidigital number, since it uses as much as digits as its factorization.

211220021981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1152, while the sum is 29.

The spelling of 211220021981 in words is "two hundred eleven billion, two hundred twenty million, twenty-one thousand, nine hundred eighty-one".