A330630 - OEIS

%I #16 Jan 20 2020 21:29:20

%S 9,77,414,545,737,818,868,5005,9889,24642,45754,87478,974479,1774771,

%T 2735372,4085804,4549454,4658564,7673767,8541458,8671768,9251529,

%U 9478749,9642469,221131122,425393524,527111725,554535455,978909879,7476336747,8731001378,15552425551

%N Palindromic composite numbers with palindromic composite indices (in A002808).

%H Chai Wah Wu, <a href="/A330630/b330630.txt">Table of n, a(n) for n = 1..55</a>

%e The palindromic composite number 77 has palindromic composite index 55 in A002808. So 77 belongs to the present sequence.

%t composite[n_]:=FixedPoint[n+PrimePi[#]+1&,n+PrimePi[n]+1];

%t indices=Select[Range[10^6],CompositeQ[#]&&PalindromeQ[#]&&PalindromeQ[composite[#]]&];

%t terms=composite/@indices (*"composite" function defined by _Robert G. Wilson v_ at A002808*)

%Y Cf. A002808, A002113.

%K nonn,base,hard

%O 1,1

%A _Ivan N. Ianakiev_, Dec 21 2019

%E a(1)-a(32) from _Daniel Suteu_, Dec 21 2019