99778561 has 2 divisors, whose sum is σ = 99778562. Its totient is φ = 99778560.

The previous prime is 99778541. The next prime is 99778571. The reversal of 99778561 is 16587799.

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., 59582961 + 40195600 = 7719^2 + 6340^2 .

It is a cyclic number.

It is not a de Polignac number, because 99778561 - 2¹⁹ = 99254273 is a prime.

It is a super-2 number, since 2×99778561² = 19911522470461442, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 99778499 and 99778508.

It is not a weakly prime, because it can be changed into another prime (99778541) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 49889280 + 49889281.

It is an arithmetic number, because the mean of its divisors is an integer number (49889281).

It is a Proth number, since it is equal to 3045 ⋅ 2¹⁵ + 1 and 3045 < 2¹⁵.

Almost surely, 2^99778561 is an apocalyptic number.

It is an amenable number.

99778561 is a deficient number, since it is larger than the sum of its proper divisors (1).

99778561 is an equidigital number, since it uses as much as digits as its factorization.

99778561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 952560, while the sum is 52.

The square root of 99778561 is about 9988.9219138003. The cubic root of 99778561 is about 463.8160205627.

The spelling of 99778561 in words is "ninety-nine million, seven hundred seventy-eight thousand, five hundred sixty-one".