A139129 Smallest term in A005244 having exactly n distinct representations A005244(i)*A005244(j)-1.

2, 5, 129, 458, 1376, 4130, 12392, 37178, 72980, 114938, 218942, 287792

Offset

0,1

Links

Table of n, a(n) for n=0..11.

Example

a(2)=A005244(28)=129: A139128(28)=#{26*5-1,65*2-1}=2.

Maple

R:= [2, 3]: count:= 2:
for i from 4 to 500000 do
  found:= false;
  for j from 1 while R[j]^2 < i+1 do
    if i mod R[j] = R[j]-1 and
        ListTools:-BinarySearch(R, (i+1)/R[j]) <> 0   then
          found:= true; break
     fi
  od;
  if found then R:= [op(R), i]; count:= count+1;
  fi
od:
f:= proc(n) local t, i, j, x, L;
  x:= R[n]+1:
  L:= R[1..n-1];
  t:= 0:
  for i from 1 while R[i]^2 < x do
    if x mod R[i] = 0 and ListTools:-BinarySearch(L, x/R[i]) <> 0 then t:= t+1 fi
  od;
  t
end proc:
V:= Array(0..11):
for i from 1 to nops(R) do
  v:= f(i);
  if V[v] = 0 then V[v]:= R[i] fi;
od:
convert(V, list); # Robert Israel, Jun 21 2024

Crossrefs

Cf. A005244, A139128.

Sequence in context: A175978 A092922 A093865 * A139484 A088271 A236045

Adjacent sequences: A139126 A139127 A139128 * A139130 A139131 A139132

Keyword

nonn,more

Author

Reinhard Zumkeller, Apr 09 2008

Extensions

a(1) corrected and more terms from Robert Israel, Jun 21 2024

Status

approved