A378187 With p(n) = A002145(n) = n-th non-Pythagorean prime, a(n) is the least k such p(n) + k is a non-Pythagorean prime and 2 p(n) + k - 3 is a Pythagorean prime; and a(n) = 0 if there is no such k.

4, 12, 12, 12, 24, 12, 24, 12, 12, 36, 12, 24, 48, 24, 60, 12, 48, 72, 12, 36, 192, 12, 60, 24, 12, 48, 12, 12, 108, 48, 60, 24, 72, 72, 168, 36, 24, 12, 84, 48, 24, 48, 108, 24, 24, 36, 12, 12, 12, 24, 60, 48, 60, 156, 48, 60, 84, 12, 24, 60, 84, 12, 84, 36

Offset

1,1

Links

Table of n, a(n) for n=1..64.

Example

3 + 4 = 7, the least non-Pythagorean prime after 3,
and 3 + 7 - 3 = 7, a Pythagorean prime, so a(1) = 4.

Mathematica

s = Select[Prime[Range[450]], Mod[#, 4] == 3 &]
a[n_] := Select[Range[200],  MemberQ[s, s[[n]] + #] && PrimeQ[2 s[[n]] + # - 3] &, 1]
Flatten[Table[a[n], {n, 1, 140}]]

Crossrefs

Cf. A000041, A002144, A002145, A378186.

Sequence in context: A063608 A074258 A253137 * A120213 A005886 A096442

Adjacent sequences: A378184 A378185 A378186 * A378188 A378189 A378190

Keyword

nonn

Author

Clark Kimberling, Jan 13 2025

Status

approved