A379014 Least number k such that prime(n) + prime(k) is a multiple of n, or -1 if no such number exists.

1, 2, 4, 3, 8, 3, 5, 3, 6, 5, 1, 5, 5, 6, 6, 5, 14, 5, 15, 10, 5, 11, 26, 4, 2, 2, 3, 3, 4, 4, 17, 10, 18, 11, 18, 10, 34, 27, 19, 19, 19, 10, 19, 20, 21, 11, 20, 7, 19, 20, 21, 21, 111, 8, 21, 7, 21, 8, 65, 8, 23, 7, 20, 21, 68, 6, 20, 2, 19, 20, 1, 21, 20, 20

Offset: 1

Author

Jean-Marc Rebert, Dec 13 2024

Keywords

• nonn

Comments

Indices n where a(n)=1 correspond with terms of A092044. - Bill McEachen, Dec 21 2024

Crossrefs

Cf. A000040, A000720, A068901, A294639.

Programs

Mathematica

a[n_]:=Module[{k=1},While[!Divisible[Prime[n]+Prime[k],n], k++]; k]; Array[a,74] (* Stefano Spezia, Dec 13 2024 *)

PARI

a(n) = my(k=1, p=prime(n)); while ((p+prime(k)) % n, k++); k; \\ Michel Marcus, Dec 13 2024

Formula

a(n) = A000720(A294639(n)). - Pontus von Brömssen, Dec 13 2024