A138026 Numbers k where A121561(k) = 3.

122, 123, 148, 190, 208, 209, 220, 221, 250, 292, 302, 303, 326, 327, 346, 418, 430, 476, 477, 518, 519, 532, 533, 538, 539, 556, 586, 628, 629, 640, 670, 671, 700, 718, 782, 783, 796, 806, 807, 820, 838, 848, 849, 872, 873, 896, 897, 902, 903, 928, 962

Offset: 1

Author

Robert G. Wilson v, Feb 27 2008

Keywords

• nonn

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A121561, A093515, A093513, A138027.

Programs

Maple

filter:= proc(n)
  local t;
  t:= n-prevprime(n+1);
  if t <= 1 then return false fi;
  t:= t-prevprime(t+1);
  if t <= 1 then return false fi;
  isprime(t) or isprime(t-1)
end proc:
select(filter,[$2..1000]); # Robert Israel, Jan 15 2019

Mathematica

LrgstPrm[n_] := Block[{k = n}, While[ !PrimeQ@k, k-- ]; k]; f[n_] := Block[{c = 0, d = n}, While[d > 1, d = d - LrgstPrm@ d; c++ ]; c]; lst = {}; Do[ If[f@n == 3, AppendTo[lst,n]], {n, 10^3}]; lst