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 A069615 #11 May 21 2025 18:57:45 %S A069615 3,31,131,1319,21319,213193,12213193,122131939,1122131939, %T A069615 112213193957,27112213193957,271122131939573,3271122131939573, %U A069615 327112213193957339,2327112213193957339,232711221319395733969,13232711221319395733969 %N A069615 a(1) = 3; a(2n) = smallest prime starting (in the most significant digits) with a(2n-1) (i.e., as a right concatenation of a(2n-1) and a number with no insignificant zeros); a(2n+1) = smallest prime ending in (the least significant digits) a(2n-1). Alternate left and right concatenation yielding primes. %e A069615 a(4) = 1319 starting with a(3) = 131 and a(5) = 21319 ending in a(4) = 1319. %Y A069615 Cf. A053582, A069605, A069606, A069607, A069608, A069609, A069610, A069611, A069613, A069614. %K A069615 nonn,base,more %O A069615 1,1 %A A069615 _Amarnath Murthy_, Mar 27 2002 %E A069615 More terms from Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Mar 30 2003