OFFSET
1,2
LINKS
Michael De Vlieger, Table of n, a(n) for n = 1..10000
EXAMPLE
a(10)=22 because 22 is the tenth deficient number which is palindromic also.
MATHEMATICA
Select[Range@ 900, And[DivisorSigma[1, #] < 2 #, PalindromeQ@ #] &] (* Michael De Vlieger, Nov 08 2017 *)
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 *)
PROG
(PARI) isok(n) = (sigma(n) < 2*n) && (d=digits(n)) && (Vecrev(d) == d); \\ Michel Marcus, Nov 08 2017
CROSSREFS
KEYWORD
easy,nonn,base,changed
AUTHOR
Shyam Sunder Gupta, Oct 14 2004
STATUS
approved