1691987993 has 2 divisors, whose sum is σ = 1691987994. Its totient is φ = 1691987992.

The previous prime is 1691987971. The next prime is 1691988043. The reversal of 1691987993 is 3997891961.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 986713744 + 705274249 = 31412^2 + 26557^2 .

It is a cyclic number.

It is not a de Polignac number, because 1691987993 - 2¹⁶ = 1691922457 is a prime.

It is not a weakly prime, because it can be changed into another prime (1691987903) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 845993996 + 845993997.

It is an arithmetic number, because the mean of its divisors is an integer number (845993997).

Almost surely, 2^1691987993 is an apocalyptic number.

It is an amenable number.

1691987993 is a deficient number, since it is larger than the sum of its proper divisors (1).

1691987993 is an equidigital number, since it uses as much as digits as its factorization.

1691987993 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6613488, while the sum is 62.

The square root of 1691987993 is about 41133.7816520679. The cubic root of 1691987993 is about 1191.6052983627.

The spelling of 1691987993 in words is "one billion, six hundred ninety-one million, nine hundred eighty-seven thousand, nine hundred ninety-three".