21061609 has 2 divisors, whose sum is σ = 21061610. Its totient is φ = 21061608.

The previous prime is 21061603. The next prime is 21061613. The reversal of 21061609 is 90616012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15642025 + 5419584 = 3955^2 + 2328^2 .

It is a cyclic number.

It is not a de Polignac number, because 21061609 - 2⁹ = 21061097 is a prime.

It is equal to p_1333645 and since 21061609 and 1333645 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (21061603) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10530804 + 10530805.

It is an arithmetic number, because the mean of its divisors is an integer number (10530805).

Almost surely, 2^21061609 is an apocalyptic number.

It is an amenable number.

21061609 is a deficient number, since it is larger than the sum of its proper divisors (1).

21061609 is an equidigital number, since it uses as much as digits as its factorization.

21061609 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 648, while the sum is 25.

The square root of 21061609 is about 4589.2928649194. The cubic root of 21061609 is about 276.1619551117.

The spelling of 21061609 in words is "twenty-one million, sixty-one thousand, six hundred nine".