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 A123132 #22 Feb 26 2024 01:56:27 %S A123132 12,13,22,15,1213,17,32,23,1215,111,2213,113,1217,1315,42,117,1223, %T A123132 119,2215,1317,12111,123,3213,25,12113,33,2217,129,121315,131,52, %U A123132 13111,12117,1517,2223,137,12119,13113,3215,141,121317,143,22111,2315,12123 %N A123132 Describe prime factorization of n (primes in ascending order and with repetition) (method A - initial term is 2). %C A123132 Method A = 'frequency' followed by 'digit'-indication. Say 'what you see' in prime factors of n, n>1. %H A123132 Paolo P. Lava, <a href="/A123132/b123132.txt">Table of n, a(n) for n = 2..10000</a> %H A123132 A. Frank & P. Jacqueroux, <a href="http://www.paulcooijmans.com/others/intcontest.pdf">International Contest</a>, 2001. %e A123132 2 has "one 2" in its prime decomposition, so a(2)=12. %e A123132 3 has "one 3" in its prime decomposition, so a(3)=13. %e A123132 4=2*2 has "two 2" in its prime decomposition, so a(4)=22. %e A123132 5 has "one 5" in its prime decomposition, so a(5)=15. %e A123132 6=2*3 has "one 2 and one 3" in its prime decomposition, so a(6)=1213. %e A123132 ..... %t A123132 a[n_] := FromDigits@ Flatten@ IntegerDigits[ Reverse /@ FactorInteger@ n]; a/@ Range[2,30] (* _Giovanni Resta_, Jun 16 2013 *) %o A123132 (PARI) for(n=2,25,factn=factor(n); for(i=1,omega(n),print1(factn[i,2],factn[i,1])); print1(",")) %o A123132 (PARI) a(n) = my(factn=factor(n), sout = ""); for(i=1, omega(n), sout = concat(sout, Str(factn[i, 2])); sout = concat(sout, Str(factn[i, 1]))); eval(sout); \\ _Michel Marcus_, Jun 29 2017 %Y A123132 Cf. A006751, A027746, A063850. %K A123132 nonn,base %O A123132 2,1 %A A123132 Herman Jamke (hermanjamke(AT)fastmail.fm), Sep 30 2006