2157209981 has 2 divisors, whose sum is σ = 2157209982. Its totient is φ = 2157209980.

The previous prime is 2157209959. The next prime is 2157209983. The reversal of 2157209981 is 1899027512.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1587624025 + 569585956 = 39845^2 + 23866^2 .

It is a cyclic number.

It is not a de Polignac number, because 2157209981 - 2¹⁰ = 2157208957 is a prime.

It is a super-2 number, since 2×2157209981² = 9307109804252040722, which contains 22 as substring.

Together with 2157209983, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (2157209983) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1078604990 + 1078604991.

It is an arithmetic number, because the mean of its divisors is an integer number (1078604991).

Almost surely, 2^2157209981 is an apocalyptic number.

It is an amenable number.

2157209981 is a deficient number, since it is larger than the sum of its proper divisors (1).

2157209981 is an equidigital number, since it uses as much as digits as its factorization.

2157209981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 90720, while the sum is 44.

The square root of 2157209981 is about 46445.7746302072. The cubic root of 2157209981 is about 1292.1040081276.

The spelling of 2157209981 in words is "two billion, one hundred fifty-seven million, two hundred nine thousand, nine hundred eighty-one".