1251906991 has 2 divisors, whose sum is σ = 1251906992. Its totient is φ = 1251906990.

The previous prime is 1251906989. The next prime is 1251907009. The reversal of 1251906991 is 1996091521.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 1251906991 - 2¹ = 1251906989 is a prime.

It is a super-2 number, since 2×1251906991² = 3134542228229348162, which contains 22 as substring.

Together with 1251906989, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1251906961) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 625953495 + 625953496.

It is an arithmetic number, because the mean of its divisors is an integer number (625953496).

Almost surely, 2^1251906991 is an apocalyptic number.

1251906991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1251906991 is an equidigital number, since it uses as much as digits as its factorization.

1251906991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 43740, while the sum is 43.

The square root of 1251906991 is about 35382.2977066216. The cubic root of 1251906991 is about 1077.7648650213.

The spelling of 1251906991 in words is "one billion, two hundred fifty-one million, nine hundred six thousand, nine hundred ninety-one".