21121661 has 8 divisors (see below), whose sum is σ = 23160000. Its totient is φ = 19103040.

The previous prime is 21121651. The next prime is 21121663. The reversal of 21121661 is 16612112.

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

It is not a de Polignac number, because 21121661 - 2¹⁰ = 21120637 is a prime.

It is a super-2 number, since 2×21121661² = 892249126797842, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21121663) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2636 + ... + 7013.

It is an arithmetic number, because the mean of its divisors is an integer number (2895000).

Almost surely, 2^21121661 is an apocalyptic number.

It is an amenable number.

21121661 is a deficient number, since it is larger than the sum of its proper divisors (2038339).

21121661 is a wasteful number, since it uses less digits than its factorization.

21121661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9859.

The product of its digits is 144, while the sum is 20.

The square root of 21121661 is about 4595.8308280440. The cubic root of 21121661 is about 276.4241753571.

Adding to 21121661 its reverse (16612112), we get a palindrome (37733773).

It can be divided in two parts, 2112 and 1661, that added together give a palindrome (3773).

The spelling of 21121661 in words is "twenty-one million, one hundred twenty-one thousand, six hundred sixty-one".