13656721 has 6 divisors (see below), whose sum is σ = 14788230. Its totient is φ = 12606048.

The previous prime is 13656697. The next prime is 13656739. The reversal of 13656721 is 12765631.

13656721 = T₉₈ + T₉₉ + ... + T₄₃₅.

It can be written as a sum of positive squares in 3 ways, for example, as 261121 + 13395600 = 511^2 + 3660^2 .

It is not a de Polignac number, because 13656721 - 2⁵ = 13656689 is a prime.

It is the 3696-th Hogben number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (13656761) by changing a digit.

It is a nontrivial repunit in base 3695.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 40236 + ... + 40573.

It is an arithmetic number, because the mean of its divisors is an integer number (2464705).

Almost surely, 2^13656721 is an apocalyptic number.

It is an amenable number.

13656721 is a deficient number, since it is larger than the sum of its proper divisors (1131509).

13656721 is an equidigital number, since it uses as much as digits as its factorization.

13656721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 80835 (or 80822 counting only the distinct ones).

The product of its digits is 7560, while the sum is 31.

The square root of 13656721 is about 3695.5001014748. The cubic root of 13656721 is about 239.0280191003.

The spelling of 13656721 in words is "thirteen million, six hundred fifty-six thousand, seven hundred twenty-one".