A084983 Palindromes made of only prime digits.

2, 3, 5, 7, 22, 33, 55, 77, 222, 232, 252, 272, 323, 333, 353, 373, 525, 535, 555, 575, 727, 737, 757, 777, 2222, 2332, 2552, 2772, 3223, 3333, 3553, 3773, 5225, 5335, 5555, 5775, 7227, 7337, 7557, 7777, 22222, 22322, 22522, 22722, 23232, 23332, 23532, 23732, 25252, 25352

Offset: 1

Author

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

Keywords

• nonn
• base

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..1000

Crossrefs

Intersection of A002113 and A046034.

Programs

Mathematica

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 *)

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

Extensions

Terms a(33) and beyond from Andrew Howroyd, Jan 27 2020