215530781 has 2 divisors, whose sum is σ = 215530782. Its totient is φ = 215530780.

The previous prime is 215530771. The next prime is 215530801. The reversal of 215530781 is 187035512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 202606756 + 12924025 = 14234^2 + 3595^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-215530781 is a prime.

It is a super-2 number, since 2×215530781² = 92907035116939922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (215530771) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 107765390 + 107765391.

It is an arithmetic number, because the mean of its divisors is an integer number (107765391).

Almost surely, 2^215530781 is an apocalyptic number.

It is an amenable number.

215530781 is a deficient number, since it is larger than the sum of its proper divisors (1).

215530781 is an equidigital number, since it uses as much as digits as its factorization.

215530781 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 8400, while the sum is 32.

The square root of 215530781 is about 14680.9666234891. The cubic root of 215530781 is about 599.5652229873.

The spelling of 215530781 in words is "two hundred fifteen million, five hundred thirty thousand, seven hundred eighty-one".