1217931721 has 2 divisors, whose sum is σ = 1217931722. Its totient is φ = 1217931720.

The previous prime is 1217931643. The next prime is 1217931769. The reversal of 1217931721 is 1271397121.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 884467600 + 333464121 = 29740^2 + 18261^2 .

It is an emirp because it is prime and its reverse (1271397121) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1217931721 - 2⁷ = 1217931593 is a prime.

It is not a weakly prime, because it can be changed into another prime (1217932721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 608965860 + 608965861.

It is an arithmetic number, because the mean of its divisors is an integer number (608965861).

Almost surely, 2^1217931721 is an apocalyptic number.

It is an amenable number.

1217931721 is a deficient number, since it is larger than the sum of its proper divisors (1).

1217931721 is an equidigital number, since it uses as much as digits as its factorization.

1217931721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5292, while the sum is 34.

The square root of 1217931721 is about 34898.8785063360. The cubic root of 1217931721 is about 1067.9255586549.

The spelling of 1217931721 in words is "one billion, two hundred seventeen million, nine hundred thirty-one thousand, seven hundred twenty-one".