1990978501 has 4 divisors (see below), whose sum is σ = 1992318912. Its totient is φ = 1989638092.

The previous prime is 1990978453. The next prime is 1990978513. The reversal of 1990978501 is 1058790991.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 1058790991 = 17 ⋅62281823.

It is a cyclic number.

It is not a de Polignac number, because 1990978501 - 2⁷ = 1990978373 is a prime.

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 Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1997978501) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 667975 + ... + 670948.

It is an arithmetic number, because the mean of its divisors is an integer number (498079728).

Almost surely, 2^1990978501 is an apocalyptic number.

It is an amenable number.

1990978501 is a deficient number, since it is larger than the sum of its proper divisors (1340411).

1990978501 is a wasteful number, since it uses less digits than its factorization.

1990978501 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1340410.

The product of its (nonzero) digits is 204120, while the sum is 49.

The square root of 1990978501 is about 44620.3821252127. The cubic root of 1990978501 is about 1258.0237982714.

The spelling of 1990978501 in words is "one billion, nine hundred ninety million, nine hundred seventy-eight thousand, five hundred one".