1265801998 has 4 divisors (see below), whose sum is σ = 1898703000. Its totient is φ = 632900998.

The previous prime is 1265801939. The next prime is 1265802011. The reversal of 1265801998 is 8991085621.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 8991085621 = 7 ⋅1284440803.

It is a Smith number, since the sum of its digits (49) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 316450498 + ... + 316450501.

It is an arithmetic number, because the mean of its divisors is an integer number (474675750).

Almost surely, 2^1265801998 is an apocalyptic number.

1265801998 is a deficient number, since it is larger than the sum of its proper divisors (632901002).

1265801998 is an equidigital number, since it uses as much as digits as its factorization.

1265801998 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 632901001.

The product of its (nonzero) digits is 311040, while the sum is 49.

The square root of 1265801998 is about 35578.1112202433. Note that the first 3 decimals coincide. The cubic root of 1265801998 is about 1081.7376001286.

The spelling of 1265801998 in words is "one billion, two hundred sixty-five million, eight hundred one thousand, nine hundred ninety-eight".