1491631721 has 2 divisors, whose sum is σ = 1491631722. Its totient is φ = 1491631720.

The previous prime is 1491631693. The next prime is 1491631789. The reversal of 1491631721 is 1271361941.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 859662400 + 631969321 = 29320^2 + 25139^2 .

It is a cyclic number.

It is not a de Polignac number, because 1491631721 - 2¹⁸ = 1491369577 is a prime.

It is not a weakly prime, because it can be changed into another prime (1491631021) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 745815860 + 745815861.

It is an arithmetic number, because the mean of its divisors is an integer number (745815861).

Almost surely, 2^1491631721 is an apocalyptic number.

It is an amenable number.

1491631721 is a deficient number, since it is larger than the sum of its proper divisors (1).

1491631721 is an equidigital number, since it uses as much as digits as its factorization.

1491631721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9072, while the sum is 35.

The square root of 1491631721 is about 38621.6483464909. The cubic root of 1491631721 is about 1142.5815409118.

The spelling of 1491631721 in words is "one billion, four hundred ninety-one million, six hundred thirty-one thousand, seven hundred twenty-one".