cp's OEIS Frontend

A359122 Index of prime(n) in A068811, or -1 if prime(n) is missing from A068811.

%I A359122 #17 Dec 18 2022 21:49:12
%S A359122 -1,1,2,3,4,-1,5,-1,-1,6,-1,-1,7,-1,8,9,10,-1,-1,11,-1,-1,12,13,14,-1,
%T A359122 -1,-1,-1,15,-1,-1,16,-1,-1,-1,-1,-1,-1,17,18,-1,19,-1,-1,-1,-1,-1,20,
%U A359122 -1,-1,21,-1,-1,22,-1,-1,-1,-1,23,-1,-1,-1,-1,-1,24,-1,-1,25,-1,26,27,-1
%N A359122 Index of prime(n) in A068811, or -1 if prime(n) is missing from A068811.
%H A359122 Michael De Vlieger, <a href="/A359122/b359122.txt">Table of n, a(n) for n = 1..10000</a>
%H A359122 Michael De Vlieger, <a href="/A359122/a359122.png">Raster showing a(n) > 0 in black else white</a>, n = 1..10^6, in rows of 1000 pixels.
%e A359122 Prime(4) = 7 is the third term in A068811, so a(4) = 3.
%e A359122 Prime(6) = 13 is missing from A068811, so a(6) = -1.
%t A359122 c = 1; Reap[Do[Sow@ If[PrimeQ[10^(1 + Floor@ Log10[#]) - #], c++, -1] &[Prime[n]], {n, 73}]][[-1, -1]] (* or, generate nn <= 10^6 terms of this sequence from the bitmap: *)
%t A359122 Block[{nn = 10^4, s = Flatten@ ImageData[Import["https://oeis.org/A359122/a359122.png"]] /. {1. -> 0, 0. -> 1}, c}, c = 1; Map[If[# == 0, -1, c++] &, s[[1 ;; nn]]]] (* _Michael De Vlieger_, Dec 18 2022 *)
%Y A359122 Cf. A068811, A359121.
%K A359122 sign
%O A359122 1,3
%A A359122 _N. J. A. Sloane_, Dec 18 2022