A084983 - OEIS

%I #8 Jan 28 2020 15:21:09

%S 2,3,5,7,22,33,55,77,222,232,252,272,323,333,353,373,525,535,555,575,

%T 727,737,757,777,2222,2332,2552,2772,3223,3333,3553,3773,5225,5335,

%U 5555,5775,7227,7337,7557,7777,22222,22322,22522,22722,23232,23332,23532,23732,25252,25352

%N Palindromes made of only prime digits.

%H Andrew Howroyd, <a href="/A084983/b084983.txt">Table of n, a(n) for n = 1..1000</a>

%t With[{p = Prime@ Range@ PrimePi@ 9}, Array[If[OddQ@ #1, Map[FromDigits@ Join[#, Reverse@ Most@ #] &, #2], Map[FromDigits@ Join[#, Reverse@ #] &, #2]] & @@ {#, Tuples[p, {Ceiling[#/2]}]} &, 5]] // Flatten (* _Michael De Vlieger_, Jan 28 2020 *)

%o (PARI) a(n)={my(k=4); while(n>2*k, n-=2*k; k*=4); my(v=[d*2+1+(!d)|d<-digits(k+n-1,4)]); fromdigits(concat(v[2..#v-(n<=k)], Vecrev(v[2..#v])))} \\ _Andrew Howroyd_, Jan 27 2020

%Y Intersection of A002113 and A046034.

%K nonn,base

%O 1,1

%A Meenakshi Srikanth (menakan_s(AT)yahoo.com), Jun 27 2003

%E Terms a(33) and beyond from _Andrew Howroyd_, Jan 27 2020