81219709 has 4 divisors (see below), whose sum is σ = 82132380. Its totient is φ = 80307040.

The previous prime is 81219707. The next prime is 81219757. The reversal of 81219709 is 90791218.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 30140100 + 51079609 = 5490^2 + 7147^2 .

It is a cyclic number.

It is not a de Polignac number, because 81219709 - 2¹ = 81219707 is a prime.

It is a super-2 number, since 2×81219709² = 13193282260089362, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81219701) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 456202 + ... + 456379.

It is an arithmetic number, because the mean of its divisors is an integer number (20533095).

Almost surely, 2^81219709 is an apocalyptic number.

81219709 is a gapful number since it is divisible by the number (89) formed by its first and last digit.

It is an amenable number.

81219709 is a deficient number, since it is larger than the sum of its proper divisors (912671).

81219709 is an equidigital number, since it uses as much as digits as its factorization.

81219709 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 912670.

The product of its (nonzero) digits is 9072, while the sum is 37.

The square root of 81219709 is about 9012.1977896626. The cubic root of 81219709 is about 433.0657218803.

The spelling of 81219709 in words is "eighty-one million, two hundred nineteen thousand, seven hundred nine".