1781221987 has 2 divisors, whose sum is σ = 1781221988. Its totient is φ = 1781221986.

The previous prime is 1781221979. The next prime is 1781221997. The reversal of 1781221987 is 7891221871.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 1781221987 - 2³ = 1781221979 is a prime.

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, 890610993 + 890610994.

It is an arithmetic number, because the mean of its divisors is an integer number (890610994).

Almost surely, 2^1781221987 is an apocalyptic number.

1781221987 is a deficient number, since it is larger than the sum of its proper divisors (1).

1781221987 is an equidigital number, since it uses as much as digits as its factorization.

1781221987 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 112896, while the sum is 46.

The square root of 1781221987 is about 42204.5256696483. The cubic root of 1781221987 is about 1212.1955418233.

The spelling of 1781221987 in words is "one billion, seven hundred eighty-one million, two hundred twenty-one thousand, nine hundred eighty-seven".