61809721 has 4 divisors (see below), whose sum is σ = 63480292. Its totient is φ = 60139152.

The previous prime is 61809703. The next prime is 61809731. The reversal of 61809721 is 12790816.

It is a happy number.

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 55875625 + 5934096 = 7475^2 + 2436^2 .

It is a cyclic number.

It is not a de Polignac number, because 61809721 - 2⁷ = 61809593 is a prime.

It is a super-2 number, since 2×61809721² = 7640883220195682, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (61809731) 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, 835230 + ... + 835303.

It is an arithmetic number, because the mean of its divisors is an integer number (15870073).

Almost surely, 2^61809721 is an apocalyptic number.

It is an amenable number.

61809721 is a deficient number, since it is larger than the sum of its proper divisors (1670571).

61809721 is a wasteful number, since it uses less digits than its factorization.

61809721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1670570.

The product of its (nonzero) digits is 6048, while the sum is 34.

The square root of 61809721 is about 7861.9158606538. The cubic root of 61809721 is about 395.3838516116.

The spelling of 61809721 in words is "sixty-one million, eight hundred nine thousand, seven hundred twenty-one".