A098897 - OEIS

%I #14 Nov 14 2024 18:14:20

%S 1,2,3,4,5,7,8,9,11,22,33,44,55,77,99,101,111,121,131,141,151,161,171,

%T 181,191,202,212,232,242,262,292,303,313,323,333,343,353,363,373,383,

%U 393,404,424,434,454,484,494,505,515,525,535,545,555,565,575,585,595

%N Palindromic deficient numbers.

%H Michael De Vlieger, <a href="/A098897/b098897.txt">Table of n, a(n) for n = 1..10000</a>

%e a(10)=22 because 22 is the tenth deficient number which is palindromic also.

%t Select[Range@ 900, And[DivisorSigma[1, #] < 2 #, PalindromeQ@ #] &] (* _Michael De Vlieger_, Nov 08 2017 *)

%t nxtPal[n_]:=With[{c=Join[{2},Flatten[Table[{10 10^d,11 10^d},{d,0,10}]]]},SelectFirst[n+c,PalindromeQ]]; Join[{1,2,3,4,5,7,8},Select[ NestList[ nxtPal[#]&,9,100],DivisorSigma[1,#]<2#&]] (* _Harvey P. Dale_, Nov 14 2024 *)

%o (PARI) isok(n) = (sigma(n) < 2*n) && (d=digits(n)) && (Vecrev(d) == d); \\ _Michel Marcus_, Nov 08 2017

%Y Intersection of A002113 and A005100.

%K easy,nonn,base,changed

%O 1,2

%A _Shyam Sunder Gupta_, Oct 14 2004