cp's OEIS Frontend

A196788 a(n) is the first occurrence of n in A196697.

%I A196788 #20 Jan 10 2023 11:38:38
%S A196788 1,1805,133,2,3,4,5,13,6,9,8,10,19,16,32,24,74,30,18,60,168,20,42,90,
%T A196788 180,210,186,408,144,1020,1050,900,2520,3348,2850,5520,3390,774,5760
%N A196788 a(n) is the first occurrence of n in A196697.
%C A196788 a(39+k) > 9594, for any k >= 1. It is getting much harder for n>39. It took the Mathematica program weeks to get the first 39 items.
%e A196788 A196697(1)=1, a(1)=1;
%e A196788 A196697(2)=4, a(4)=2;
%e A196788 ...
%e A196788 A196697(1805)=2, a(2)=1805; (for any k<1805, A196697(k)<>2)
%t A196788 b = 2; max = 39; Array[fa, max]; Do[
%t A196788 fa[k] = 0, {k, 1, max}]; filled = 0; i = 0; While[filled < max, i++;
%t A196788 c1 = b^i; cs = {};
%t A196788 Do[c2 = b^j; cp = c1 + c2 + 1; If[PrimeQ[cp], cs = Union[cs, {cp}]];
%t A196788   cp = c1 + c2 - 1; If[PrimeQ[cp], cs = Union[cs, {cp}]];
%t A196788   cp = c1 - c2 + 1; If[PrimeQ[cp], cs = Union[cs, {cp}]];
%t A196788   cp = c1 - c2 - 1;
%t A196788   If[PrimeQ[cp], cs = Union[cs, {cp}]], {j, 0, i - 1}];
%t A196788 ct = Length[cs];
%t A196788 If[ct <= max, If[fa[ct] == 0, fa[ct] = i; filled++]]]; Table[
%t A196788 fa[k], {k, 1, max}]
%Y A196788 Cf. A196697.
%K A196788 nonn,more
%O A196788 1,2
%A A196788 _Lei Zhou_, Oct 06 2011