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A281879
Non-palindromic numbers k such that sigma(k) | sigma(R(k)), where R(k) is the digit reversal of k.
2
15, 16, 17, 59, 129, 165, 176, 187, 205, 273, 276, 299, 429, 446, 478, 528, 599, 825, 1034, 1043, 1135, 1209, 1239, 1515, 1561, 1565, 1616, 1651, 1665, 1717, 1776, 1887, 2086, 2165, 2178, 2255, 2455, 2515, 2618, 2739, 2829, 3489, 4008, 4064, 4475, 4604, 5346, 5795
OFFSET
1,1
EXAMPLE
a(1) = 15 because sigma(51) / sigma(15) = 72 / 24 = 3;
a(2) = 16 because sigma(61) / sigma(16) = 62 / 31 = 2;
a(3) = 17 because sigma(71) / sigma(17) = 72 / 18 = 4.
MAPLE
with(numtheory): T:=proc(w) local x, y, z; x:=w; y:=0;
for z from 1 to ilog10(x)+1 do y:=10*y+(x mod 10); x:=trunc(x/10); od; y; end:
P:=proc(q) local n; for n from 1 to q do
if n<>T(n) then if type(sigma(T(n))/sigma(n), integer) then print(n); fi; fi; od; end: P(10^6);
MATHEMATICA
Select[Range[6000], !PalindromeQ[#]&&Mod[DivisorSigma[1, IntegerReverse[#]], DivisorSigma[ 1, #]] ==0&] (* Harvey P. Dale, Dec 19 2023 *)
CROSSREFS
KEYWORD
nonn,easy,base
AUTHOR
Paolo P. Lava, Feb 01 2017
STATUS
approved