1291991 has 2 divisors, whose sum is σ = 1291992.
Its totient is φ = 1291990.
The previous prime is 1291967. The next prime is 1291999. The reversal of 1291991 is 1991921.
It is a strong prime.
It is an emirp because it is prime and its reverse (1991921) is a distict prime.
It is a cyclic number.
It is a de Polignac number, because none of the positive numbers 2k-1291991 is a prime.
It is a Chen prime.
It is an Ulam number.
It is a congruent number.
It is not a weakly prime, because it can be changed into another prime (1291999) by changing a digit.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 645995 + 645996.
It is an arithmetic number, because the mean of its divisors is an integer number (645996).
21291991 is an apocalyptic number.
1291991 is a deficient number, since it is larger than the sum of its proper divisors (1).
1291991 is an equidigital number, since it uses as much as digits as its factorization.
1291991 is an evil number, because the sum of its binary digits is even.
The product of its digits is 1458, while the sum is 32.
The square root of 1291991 is about 1136.6578201024.
The cubic root of 1291991 is about 108.9146991356.
The spelling of 1291991 in words is "one million, two hundred ninety-one thousand, nine hundred ninety-one".