1781221997 has 2 divisors, whose sum is σ = 1781221998. Its totient is φ = 1781221996.

The previous prime is 1781221987. The next prime is 1781222017. The reversal of 1781221997 is 7991221871.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1375964836 + 405257161 = 37094^2 + 20131^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1781221997 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1781221907) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 890610998 + 890610999.

It is an arithmetic number, because the mean of its divisors is an integer number (890610999).

Almost surely, 2^1781221997 is an apocalyptic number.

It is an amenable number.

1781221997 is a deficient number, since it is larger than the sum of its proper divisors (1).

1781221997 is an equidigital number, since it uses as much as digits as its factorization.

1781221997 is an evil number, because the sum of its binary digits is even.

The product of its digits is 127008, while the sum is 47.

The square root of 1781221997 is about 42204.5257881190. The cubic root of 1781221997 is about 1212.1955440918.

The spelling of 1781221997 in words is "one billion, seven hundred eighty-one million, two hundred twenty-one thousand, nine hundred ninety-seven".