A115897 - OEIS

%I #19 Jul 15 2021 21:23:56

%S 1,2,3,4,10,11,21,49,92,101,115,131,145,186,200,201,206,207,221,226,

%T 227,240,272,302,310,313,327,342,344,370,374,388,403,406,409,413,419,

%U 425,439,449,880,948,1015,1055,1132,1165,1385,1443,1680,1755,1785

%N Numbers k such that sigma(k) + phi(k) is a palindrome.

%H Michael De Vlieger, <a href="/A115897/b115897.txt">Table of n, a(n) for n = 1..5000</a>

%e sigma(1055) + phi(1055) = 1272 + 840 = 2112.

%t Select[Range@ 1800, Reverse@ # == # &@ IntegerDigits[DivisorSigma[1, #] + EulerPhi@ #] &] (* _Michael De Vlieger_, Jul 22 2016 *)

%t Select[Range[2000],PalindromeQ[DivisorSigma[1,#]+EulerPhi[#]]&] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Mar 29 2020 *)

%o (PARI) ispal(n)=n=digits(n); Vecrev(n)==n

%o is(n,f=factor(n))=ispal(sigma(f)+eulerphi(f)) \\ _Charles R Greathouse IV_, Jul 22 2016

%Y Cf. A115895, A115896.

%K nonn,base

%O 1,2

%A _Giovanni Resta_, Feb 06 2006