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 A261618 #50 Sep 08 2022 08:46:13 %S A261618 121,232,343,454,565,676,787,898,9109,101110,111211,121312,131413, %T A261618 141514,151615,161716,171817,181918,192019,202120,212221,222322, %U A261618 232423,242524,252625,262726,272827,282928,293029,303130,313231,323332,333433,343534,353635,363736 %N A261618 Concatenation of n, n+1 and n. %C A261618 787, 9109, 111211, 131413, ... are primes. - _N. J. A. Sloane_, Sep 21 2015 %H A261618 Robert Israel, <a href="/A261618/b261618.txt">Table of n, a(n) for n = 1..10000</a> %e A261618 a(1) = concatenation(1, 2, 1) = 121. %e A261618 a(10) = concatenation(10, 11, 10) = 101110. %p A261618 f:= n -> n + 10^(1+ilog10(n))*(n+1)+10^(2+ilog10(n)+ilog10(n+1))*n: %p A261618 map(f, [$1..100]); # _Robert Israel_, Dec 29 2019 %t A261618 Map[FromDigits@ Join[#1, #2, #1] & @@ IntegerDigits[#] &, Partition[Range@ 37, 2, 1]] (* _Michael De Vlieger_, Dec 29 2019 *) %o A261618 (PARI) a(n) = eval(concat(Str(n), concat(Str(n+1), Str(n)))); \\ _Michel Marcus_, Sep 10 2015 %o A261618 (Magma) [Seqint(Intseq(n) cat Intseq(n+1) cat Intseq(n)):n in [1..36]]; // _Marius A. Burtea_, Dec 29 2019 %Y A261618 Cf. A134810, A068660. %K A261618 nonn,base %O A261618 1,1 %A A261618 _José de Jesús Camacho Medina_, Sep 09 2015 %E A261618 More terms from _Michel Marcus_, Sep 10 2015