21121651 has 2 divisors, whose sum is σ = 21121652. Its totient is φ = 21121650.

The previous prime is 21121649. The next prime is 21121663. The reversal of 21121651 is 15612112.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21121651 - 2¹ = 21121649 is a prime.

It is a super-2 number, since 2×21121651² = 892248281931602, which contains 22 as substring.

Together with 21121649, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21121631) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10560825 + 10560826.

It is an arithmetic number, because the mean of its divisors is an integer number (10560826).

Almost surely, 2^21121651 is an apocalyptic number.

21121651 is a deficient number, since it is larger than the sum of its proper divisors (1).

21121651 is an equidigital number, since it uses as much as digits as its factorization.

21121651 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 120, while the sum is 19.

The square root of 21121651 is about 4595.8297401013. The cubic root of 21121651 is about 276.4241317329.

Adding to 21121651 its reverse (15612112), we get a palindrome (36733763).

The spelling of 21121651 in words is "twenty-one million, one hundred twenty-one thousand, six hundred fifty-one".