1291921806 has 64 divisors (see below), whose sum is σ = 3065518080. Its totient is φ = 355311360.

The previous prime is 1291921801. The next prime is 1291921819. The reversal of 1291921806 is 6081291921.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1291921801) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 115050 + ... + 125778.

It is an arithmetic number, because the mean of its divisors is an integer number (47898720).

Almost surely, 2^1291921806 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 1291921806, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1532759040).

1291921806 is an abundant number, since it is smaller than the sum of its proper divisors (1773596274).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

1291921806 is a wasteful number, since it uses less digits than its factorization.

1291921806 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10849.

The product of its (nonzero) digits is 15552, while the sum is 39.

The square root of 1291921806 is about 35943.3137871288. The cubic root of 1291921806 is about 1089.1275475205.

The spelling of 1291921806 in words is "one billion, two hundred ninety-one million, nine hundred twenty-one thousand, eight hundred six".