A375261 Smallest n-digit reversible prime with only prime digits.
2, 37, 337, 3257, 32233, 322573, 3222223, 32235223, 322222223, 3222222257, 32222232577, 322222232537, 3222222223333, 32222222332733, 322222222237537, 3222222222223373, 32222222222223353, 322222222222225333, 3222222222222222577, 32222222222222225573, 322222222222222233253
Offset: 1
Links
- Robert Israel, Table of n, a(n) for n = 1..243
Programs
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Maple
PD:= [2,3,5,7]: g:= proc(n) local L,d,i,x,y; L:= convert(n,base,4); d:= nops(L); x:= add(PD[L[i]+1]*10^(i-1),i=1..d); y:= add(PD[L[-i]+1]*10^(i-1),i=1..d); if isprime(x) and isprime(y) then return x fi; end proc: f:= proc(d) local k,v; for k from 4^(d-1) do v:= g(k); if v <> NULL then return v fi od end proc; f(1):= 2: map(f, [$1..30]); # Robert Israel, May 11 2025
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Python
from sympy import isprime from itertools import product def a(n): if n == 1: return 2 for first in "37": for rest in product("2357", repeat=n-1): s = first + "".join(rest) if isprime(t:=int(s)) and isprime(int(s[::-1])): return t print([a(n) for n in range(1, 22)]) # Michael S. Branicky, Aug 08 2024
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