A377319 a(n) is the smallest positive integer k such that n + k and n - k have the same number of divisors.

1, 2, 1, 1, 2, 1, 3, 3, 1, 6, 3, 2, 3, 6, 1, 1, 3, 2, 9, 5, 2, 6, 3, 3, 6, 12, 1, 4, 6, 4, 1, 5, 2, 2, 6, 2, 3, 1, 1, 8, 3, 2, 11, 3, 4, 7, 3, 1, 6, 2, 3, 1, 1, 4, 7, 9, 1, 4, 7, 4, 3, 6, 5, 2, 2, 2, 3, 6, 1, 4, 4, 4, 3, 6, 4, 9, 6, 2, 5, 5, 2, 8, 1, 3, 3, 2, 3

Offset: 4

Author

Felix Huber, Nov 17 2024

Keywords

• nonn

Comments

If the strong Goldbach conjecture is true, that every even number >= 8 is the sum of two distinct primes, then a positive integer k <= A082467(n) exists for n >= 4.

Examples

			a(8) = 2 because 10 and 6 have both four divisors. 9 and 7 have a different number of divisors.
		

Links

• Felix Huber, Table of n, a(n) for n = 4..10000

Crossrefs

Cf. A000005, A067888 , A082467, A171937, A377320, A377321.

Programs

Maple

A377319:=proc(n)
   local k;
   for k to n-1 do
      if NumberTheory:-tau(n+k)=NumberTheory:-tau(n-k) then
         return k
      fi
   od;
end proc;
seq(A377319(n),n=4..90);

Mathematica

A377319[n_] := Module[{k = 0}, While[DivisorSigma[0, ++k + n] != DivisorSigma[0, n - k]]; k];
Array[A377319, 100, 4] (* Paolo Xausa, Dec 03 2024 *)

PARI

a(n) = my(k=1); while (numdiv(n+k) != numdiv(n-k), k++); k; \\ Michel Marcus, Nov 17 2024

Formula

1 <= a(n) <= A082467(n).