817661993 has 2 divisors, whose sum is σ = 817661994. Its totient is φ = 817661992.

The previous prime is 817661981. The next prime is 817662067. The reversal of 817661993 is 399166718.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 650658064 + 167003929 = 25508^2 + 12923^2 .

It is a cyclic number.

It is not a de Polignac number, because 817661993 - 2¹⁰ = 817660969 is a prime.

It is a super-2 number, since 2×817661993² = 1337142269593464098, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (817661693) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 408830996 + 408830997.

It is an arithmetic number, because the mean of its divisors is an integer number (408830997).

Almost surely, 2^817661993 is an apocalyptic number.

It is an amenable number.

817661993 is a deficient number, since it is larger than the sum of its proper divisors (1).

817661993 is an equidigital number, since it uses as much as digits as its factorization.

817661993 is an evil number, because the sum of its binary digits is even.

The product of its digits is 489888, while the sum is 50.

The square root of 817661993 is about 28594.7896127948. The cubic root of 817661993 is about 935.0997417117.

The spelling of 817661993 in words is "eight hundred seventeen million, six hundred sixty-one thousand, nine hundred ninety-three".