215777981 has 2 divisors, whose sum is σ = 215777982. Its totient is φ = 215777980.

The previous prime is 215777963. The next prime is 215778001. The reversal of 215777981 is 189777512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 156025081 + 59752900 = 12491^2 + 7730^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-215777981 is a prime.

It is a super-2 number, since 2×215777981² = 93120274168872722, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (215777921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 107888990 + 107888991.

It is an arithmetic number, because the mean of its divisors is an integer number (107888991).

Almost surely, 2^215777981 is an apocalyptic number.

It is an amenable number.

215777981 is a deficient number, since it is larger than the sum of its proper divisors (1).

215777981 is an equidigital number, since it uses as much as digits as its factorization.

215777981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 246960, while the sum is 47.

The square root of 215777981 is about 14689.3832750051. The cubic root of 215777981 is about 599.7943563777.

The spelling of 215777981 in words is "two hundred fifteen million, seven hundred seventy-seven thousand, nine hundred eighty-one".