781729721 has 2 divisors, whose sum is σ = 781729722. Its totient is φ = 781729720.

The previous prime is 781729643. The next prime is 781729777. The reversal of 781729721 is 127927187.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 754051600 + 27678121 = 27460^2 + 5261^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-781729721 is a prime.

It is a super-2 number, since 2×781729721² = 1222202713389475682, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (781729621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 390864860 + 390864861.

It is an arithmetic number, because the mean of its divisors is an integer number (390864861).

Almost surely, 2^781729721 is an apocalyptic number.

It is an amenable number.

781729721 is a deficient number, since it is larger than the sum of its proper divisors (1).

781729721 is an equidigital number, since it uses as much as digits as its factorization.

781729721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 98784, while the sum is 44.

The square root of 781729721 is about 27959.4299119277. The cubic root of 781729721 is about 921.1963488642.

The spelling of 781729721 in words is "seven hundred eighty-one million, seven hundred twenty-nine thousand, seven hundred twenty-one".