256001661 has 32 divisors (see below), whose sum is σ = 404997120. Its totient is φ = 159434352.

The previous prime is 256001639. The next prime is 256001699. The reversal of 256001661 is 166100652.

It is a happy number.

It is not a de Polignac number, because 256001661 - 2⁶ = 256001597 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (256001561) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 21910 + ... + 31496.

It is an arithmetic number, because the mean of its divisors is an integer number (12656160).

Almost surely, 2^256001661 is an apocalyptic number.

It is an amenable number.

256001661 is a deficient number, since it is larger than the sum of its proper divisors (148995459).

256001661 is a wasteful number, since it uses less digits than its factorization.

256001661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9662 (or 9656 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 27.

The square root of 256001661 is about 16000.0519061658. The cubic root of 256001661 is about 634.9617940516.

It can be divided in two parts, 25600 and 1661, that added together give a triangular number (27261 = T₂₃₃).

The spelling of 256001661 in words is "two hundred fifty-six million, one thousand, six hundred sixty-one".