1289987661 has 4 divisors (see below), whose sum is σ = 1719983552. Its totient is φ = 859991772.

The previous prime is 1289987651. The next prime is 1289987669. The reversal of 1289987661 is 1667899821.

1289987661 is digitally balanced in base 4, because in such base it contains all the possibile digits an equal number of times.

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.

It is not a de Polignac number, because 1289987661 - 2⁷ = 1289987533 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1289987669) 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, 214997941 + ... + 214997946.

It is an arithmetic number, because the mean of its divisors is an integer number (429995888).

Almost surely, 2^1289987661 is an apocalyptic number.

It is an amenable number.

1289987661 is a deficient number, since it is larger than the sum of its proper divisors (429995891).

1289987661 is an equidigital number, since it uses as much as digits as its factorization.

1289987661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 429995890.

The product of its digits is 2612736, while the sum is 57.

The square root of 1289987661 is about 35916.3982186410. The cubic root of 1289987661 is about 1088.5837626207.

The spelling of 1289987661 in words is "one billion, two hundred eighty-nine million, nine hundred eighty-seven thousand, six hundred sixty-one".