This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A099410 #35 May 03 2024 15:02:43
%S A099410 0,2,3,5,14,176,416,2505,2759,7925,9401,10391,12105,19616,261704,
%T A099410 264539
%N A099410 Numbers k such that 2*R_k + 7 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
%C A099410 Also numbers k such that (2*10^k + 61)/9 is prime.
%C A099410 Although perhaps a degenerate case, A002275 defines R(0)=0. Thus zero belongs in this sequence since 2*0+7=7 is prime. - _Robert Price_, Oct 28 2014
%C A099410 a(15) > 10^5. - _Robert Price_, Oct 29 2014
%H A099410 Makoto Kamada, <a href="https://stdkmd.net/nrr/2/22229.htm#prime">Prime numbers of the form 22...229</a>.
%H A099410 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>
%F A099410 a(n) = A056678(n-1) + 1.
%t A099410 Do[ If[ PrimeQ[ 2(10^n - 1)/9 + 7], Print[n]], {n, 0, 5000}]
%o A099410 (Magma) [n: n in [0..500] | IsPrime((2*10^n+61) div 9)]; // _Vincenzo Librandi_, Oct 30 2014
%Y A099410 Cf. A002275, A056678, A093401.
%K A099410 nonn
%O A099410 1,2
%A A099410 _Robert G. Wilson v_, Oct 14 2004
%E A099410 Added zero and adapted Mathematica program by _Robert Price_, Oct 28 2014
%E A099410 a(10)-a(14) from Kamada data by _Robert Price_, Oct 29 2014
%E A099410 a(15)-a(16) from Kamada data by _Tyler Busby_, May 03 2024