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A196788
a(n) is the first occurrence of n in A196697.
0
1, 1805, 133, 2, 3, 4, 5, 13, 6, 9, 8, 10, 19, 16, 32, 24, 74, 30, 18, 60, 168, 20, 42, 90, 180, 210, 186, 408, 144, 1020, 1050, 900, 2520, 3348, 2850, 5520, 3390, 774, 5760
OFFSET
1,2
COMMENTS
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.
EXAMPLE
A196697(1)=1, a(1)=1;
A196697(2)=4, a(4)=2;
...
A196697(1805)=2, a(2)=1805; (for any k<1805, A196697(k)<>2)
MATHEMATICA
b = 2; max = 39; Array[fa, max]; Do[
fa[k] = 0, {k, 1, max}]; filled = 0; i = 0; While[filled < max, i++;
c1 = b^i; cs = {};
Do[c2 = b^j; cp = c1 + c2 + 1; If[PrimeQ[cp], cs = Union[cs, {cp}]];
cp = c1 + c2 - 1; If[PrimeQ[cp], cs = Union[cs, {cp}]];
cp = c1 - c2 + 1; If[PrimeQ[cp], cs = Union[cs, {cp}]];
cp = c1 - c2 - 1;
If[PrimeQ[cp], cs = Union[cs, {cp}]], {j, 0, i - 1}];
ct = Length[cs];
If[ct <= max, If[fa[ct] == 0, fa[ct] = i; filled++]]]; Table[
fa[k], {k, 1, max}]
CROSSREFS
Cf. A196697.
Sequence in context: A252676 A248063 A256027 * A252029 A250385 A345765
KEYWORD
nonn,more
AUTHOR
Lei Zhou, Oct 06 2011
STATUS
approved