21665701 has 8 divisors (see below), whose sum is σ = 23937984. Its totient is φ = 19504320.

The previous prime is 21665689. The next prime is 21665713. The reversal of 21665701 is 10756612.

21665701 = T₃₇₉₉ + T₃₈₀₀ + T₃₈₀₁.

It is an interprime number because it is at equal distance from previous prime (21665689) and next prime (21665713).

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21665701 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21665701.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21665771) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 27315 + ... + 28096.

It is an arithmetic number, because the mean of its divisors is an integer number (2992248).

Almost surely, 2^21665701 is an apocalyptic number.

21665701 is the 3801-st centered triangular number.

It is an amenable number.

21665701 is a deficient number, since it is larger than the sum of its proper divisors (2272283).

21665701 is a wasteful number, since it uses less digits than its factorization.

21665701 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 55451.

The product of its (nonzero) digits is 2520, while the sum is 28.

The square root of 21665701 is about 4654.6429508610. The cubic root of 21665701 is about 278.7774118243. Note that the first 3 decimals are identical.

It can be divided in two parts, 21665 and 701, that added together give a triangular number (22366 = T₂₁₁).

The spelling of 21665701 in words is "twenty-one million, six hundred sixty-five thousand, seven hundred one".