A391806 a(n) = least k such that the sum of the first k odd primes is divisible by n.

1, 2, 1, 2, 3, 16, 6, 2, 13, 20, 44, 40, 4, 6, 3, 38, 33, 42, 25, 60, 60, 44, 24, 40, 7, 4, 100, 6, 89, 60, 13, 38, 44, 40, 60, 42, 27, 60, 5, 186, 157, 60, 29, 54, 37, 24, 52, 40, 8, 134, 40, 38, 41, 100, 49, 6, 60, 186, 12, 60, 25, 52, 88, 40, 11, 44, 152

Offset

1,2

Links

Table of n, a(n) for n=1..67.

Mathematica

z = 1000; s[n_] := Total[Prime[1 + Range[n]]];
t = Table[s[n], {n, 1, z}]  (* A071148 *)
a[n_] := Select[Range[z], IntegerQ[t[[#]]/n] &, 1];
Flatten[Table[a[n], {n, 1, z/4}]]

Prog

(PARI) a(n) = my(k=2); while ((vecsum(primes(k))-2) % n, k++); k-1; \\ Michel Marcus, Jan 12 2026

Crossrefs

Cf. A065091, A071148, A053050.

Sequence in context: A178463 A213593 A350026 * A382273 A118888 A061678

Adjacent sequences: A391803 A391804 A391805 * A391807 A391808 A391809

Keyword

nonn

Author

Clark Kimberling, Jan 05 2026

Status

approved