721161781 has 2 divisors, whose sum is σ = 721161782. Its totient is φ = 721161780.

The previous prime is 721161761. The next prime is 721161797. The reversal of 721161781 is 187161127.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 720439281 + 722500 = 26841^2 + 850^2 .

It is an emirp because it is prime and its reverse (187161127) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-721161781 is a prime.

It is a super-2 number, since 2×721161781² = 1040148628750183922, which contains 22 as substring.

It is equal to p_37291129 and since 721161781 and 37291129 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (721161731) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360580890 + 360580891.

It is an arithmetic number, because the mean of its divisors is an integer number (360580891).

Almost surely, 2^721161781 is an apocalyptic number.

It is an amenable number.

721161781 is a deficient number, since it is larger than the sum of its proper divisors (1).

721161781 is an equidigital number, since it uses as much as digits as its factorization.

721161781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4704, while the sum is 34.

The square root of 721161781 is about 26854.4555148675. The cubic root of 721161781 is about 896.7627653362.

The spelling of 721161781 in words is "seven hundred twenty-one million, one hundred sixty-one thousand, seven hundred eighty-one".