721543681 has 2 divisors, whose sum is σ = 721543682. Its totient is φ = 721543680.

The previous prime is 721543657. The next prime is 721543687. The reversal of 721543681 is 186345127.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 383572225 + 337971456 = 19585^2 + 18384^2 .

It is an emirp because it is prime and its reverse (186345127) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 721543681 - 2¹³ = 721535489 is a prime.

It is a super-2 number, since 2×721543681² = 1041250567182059522, which contains 22 as substring.

It is a nialpdrome in base 13.

It is a self number, because there is not a number n which added to its sum of digits gives 721543681.

It is not a weakly prime, because it can be changed into another prime (721543687) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360771840 + 360771841.

It is an arithmetic number, because the mean of its divisors is an integer number (360771841).

Almost surely, 2^721543681 is an apocalyptic number.

It is an amenable number.

721543681 is a deficient number, since it is larger than the sum of its proper divisors (1).

721543681 is an equidigital number, since it uses as much as digits as its factorization.

721543681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 40320, while the sum is 37.

The square root of 721543681 is about 26861.5651256586. The cubic root of 721543681 is about 896.9210346146.

The spelling of 721543681 in words is "seven hundred twenty-one million, five hundred forty-three thousand, six hundred eighty-one".