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 A064961 #15 Apr 03 2023 10:36:10
%S A064961 1,4,7,14,43,62,293,366,2473,2892,26317,29522,344249,376259,5429539,
%T A064961 5831545,101291779,107457490,2198218819,2310909505,54720307351,
%U A064961 57128530327,1543908890351,1603146693999,48871886538151,50527531769529,1720466016680911,1772475453490311
%N A064961 Composite-then-prime recurrence; a(2n) = a(2n-1)-th composite and a(2n+1) = a(2n)-th prime and a(1) = 1.
%H A064961 Chai Wah Wu, <a href="/A064961/b064961.txt">Table of n, a(n) for n = 1..32</a>
%H A064961 Andrew R. Booker, <a href="https://t5k.org/nthprime/">The Nth Prime Page</a>
%H A064961 N. Fernandez, <a href="http://www.borve.org/primeness/FOP.html">An order of primeness, F(p)</a>
%H A064961 N. Fernandez, <a href="/A006450/a006450.html">An order of primeness</a> [cached copy, included with permission of the author]
%t A064961 Composite[n_Integer] := FixedPoint[n + PrimePi[ # ] + 1 &, n + PrimePi[n] + 1]; a = {1, 4}; b = 4; Do[ If[ !PrimeQ[b], b = Prime[b], b = Composite[b]]; a = Append[a, b], {n, 1, 23}]; a
%Y A064961 Cf. A007097, A006508 & A064960, see also A057450, A057451, A057452, A057453, A057456 & A057457 and A049076, A049077, A049078, A049079, A049080 & A049081.
%K A064961 nonn
%O A064961 1,2
%A A064961 _Robert G. Wilson v_, Oct 29 2001
%E A064961 a(24)-a(26) corrected and a(27)-a(28) added by _Chai Wah Wu_, Aug 22 2018