• 49 can be written using four 4's:

See also 113.

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49 has 3 divisors (see below), whose sum is σ = 57. Its totient is φ = 42.

The previous prime is 47. The next prime is 53. The reversal of 49 is 94.

49 = T₆ + T₇.

It is a happy number.

The square root of 49 is 7.

It is a perfect power (a square), and thus also a powerful number.

49 is nontrivially palindromic in base 6.

49 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

49 is an esthetic number in base 6, base 9, base 11 and base 15, because in such bases its adjacent digits differ by 1.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 94 = 2 ⋅47.

It is a trimorphic number since its cube, 117649, ends in 49.

It is not a de Polignac number, because 49 - 2¹ = 47 is a prime.

49 is a Gilda number.

It is a magnanimous number.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

49 is an undulating number in base 6.

49 is a modest number, since divided by 9 gives 4 as remainder.

49 is a lucky number.

It is a plaindrome in base 5, base 10, base 11, base 13, base 14 and base 15.

It is a nialpdrome in base 7, base 8, base 9, base 12 and base 16.

It is a pernicious number, because its binary representation contains a prime number (3) of ones.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 4 + ... + 10.

It is an arithmetic number, because the mean of its divisors is an integer number (19).

It is a Proth number, since it is equal to 3 ⋅ 2⁴ + 1 and 3 < 2⁴.

49 is the 7-th square number.

49 is the 4-th centered octagonal number.

It is an amenable number.

49 is a deficient number, since it is larger than the sum of its proper divisors (8).

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

With its successor (50) it forms a Ruth-Aaron pair, since the sum of their distinct prime factors is the same (7).

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

The sum of its prime factors is 14 (or 7 counting only the distinct ones).

The product of its digits is 36, while the sum is 13.

The cubic root of 49 is about 3.6593057100.

Subtracting from 49 its sum of digits (13), we obtain a triangular number (36 = T₈).

Multiplying 49 by its product of digits (36), we get a square (1764 = 42²).

Subtracting 49 from its reverse (94), we obtain a triangular number (45 = T₉).

The spelling of 49 in words is "forty-nine", and thus it is an aban number and an uban number.