cp's OEIS Frontend

A281879 Non-palindromic numbers k such that sigma(k) | sigma(R(k)), where R(k) is the digit reversal of k.

%I A281879 #20 Dec 19 2023 16:18:52
%S A281879 15,16,17,59,129,165,176,187,205,273,276,299,429,446,478,528,599,825,
%T A281879 1034,1043,1135,1209,1239,1515,1561,1565,1616,1651,1665,1717,1776,
%U A281879 1887,2086,2165,2178,2255,2455,2515,2618,2739,2829,3489,4008,4064,4475,4604,5346,5795
%N A281879 Non-palindromic numbers k such that sigma(k) | sigma(R(k)), where R(k) is the digit reversal of k.
%H A281879 Harvey P. Dale, <a href="/A281879/b281879.txt">Table of n, a(n) for n = 1..500</a>
%H A281879 Paolo P. Lava, <a href="/A281879/a281879.txt">First 250 terms with the ratio sigma(R(k))/sigma(k)</a>
%e A281879 a(1) = 15 because sigma(51) / sigma(15) = 72 / 24 = 3;
%e A281879 a(2) = 16 because sigma(61) / sigma(16) = 62 / 31 = 2;
%e A281879 a(3) = 17 because sigma(71) / sigma(17) = 72 / 18 = 4.
%p A281879 with(numtheory): T:=proc(w) local x, y, z; x:=w; y:=0;
%p A281879 for z from 1 to ilog10(x)+1 do y:=10*y+(x mod 10); x:=trunc(x/10); od; y; end:
%p A281879 P:=proc(q) local n; for n from 1 to q do
%p A281879 if n<>T(n) then if type(sigma(T(n))/sigma(n),integer) then print(n); fi; fi; od; end: P(10^6);
%t A281879 Select[Range[6000],!PalindromeQ[#]&&Mod[DivisorSigma[1,IntegerReverse[#]],DivisorSigma[ 1,#]] ==0&] (* _Harvey P. Dale_, Dec 19 2023 *)
%Y A281879 Cf. A000203, A004086, A085329, A281880.
%K A281879 nonn,easy,base
%O A281879 1,1
%A A281879 _Paolo P. Lava_, Feb 01 2017