A355785 a(n) is the least k such that A355784(k) = n, or -1 if there is no such k.

1, 2, 10, 7, 15, 21, 25, 80, 29, 19, 31, 55, 57, 37, 47, 69, 89, 172, 115, 164, 85, 109, 129, 91, 117, 207, 97, 79, 135, 184, 219, 275, 177, 121, 304, 127, 279, 211, 201, 157, 235, 281, 425, 199, 329, 389, 169, 239, 297, 365, 267, 461, 187, 217, 331, 373, 277, 327, 415, 460, 790, 325, 307, 351

Offset

0,2

Comments

a(n) is the least k such that there are exactly n primes of the form j*(k-j)+k, 1 <= j < k.

Does such a number k always exist?

Links

Robert Israel, Table of n, a(n) for n = 0..1000

Example

a(4) = 15 because 15 is the least k for which A355784(k) = 4.

Maple

V:= Array(0..100):
count:= 0:
for k from 1 while count < 101 do
  v:= f(k);
  if v > 100 then next fi;
  if V[v] = 0 then V[v]:= k; count:= count+1 fi
od:
convert(V, list);

Crossrefs

Cf. A355784.

Sequence in context: A037187 A248061 A267500 * A300016 A368559 A166542

Adjacent sequences: A355782 A355783 A355784 * A355786 A355787 A355788

Keyword

nonn

Author

J. M. Bergot and Robert Israel, Jul 16 2022

Status

approved