A346756 Lesser emirps (A109308) subtracted from their reversals.

18, 54, 36, 18, 594, 198, 792, 594, 594, 792, 792, 396, 396, 594, 594, 198, 198, 198, 7992, 180, 270, 2268, 540, 8532, 810, 6804, 1908, 7902, 360, 2358, 630, 2718, 1908, 5904, 1998, 7992, 90, 6084, 8172, 8262, 8442, 2538, 450, 8532, 7632, 7812, 7902, 2088, 270

Offset: 1

Author

George Bull, Aug 20 2021

Keywords

• nonn
• base
• look

Examples

			31 - 13 = 18, 71 - 17 = 54, 73 - 37 = 36 (distance between lesser emirps and their reversals).
		

Links

• Robert Israel, Table of n, a(n) for n = 1..10000
• Carlos Rivera, Puzzle 20. Reversible Primes, The Prime Puzzles and Problems Connection.

Crossrefs

Cf. A004086, A006567, A109308.

Programs

Maple

rev:= proc(n) local L,i;
  L:= convert(n,base,10);
  add(L[-i]*10^(i-1),i=1..nops(L));
end proc:
f:= proc(p) local r;
  if not isprime(p) then return NULL fi;
  r:= rev(p);
  if r > p and isprime(r) then r-p else NULL fi
end proc:
map(f, [seq(i,i=11 .. 10^4, 2)]); # Robert Israel, Dec 28 2023

Mathematica

f[n_] := IntegerReverse[n] - n; Map[f, Select[Range[1500], f[#] > 0 && PrimeQ[#] && PrimeQ @ IntegerReverse[#] &]] (* Amiram Eldar, Sep 08 2021 *)

PARI

rev(p) = fromdigits(Vecrev(digits(p))); \\ A004086
lista(nn) = {my(list = List()); forprime (p=1, nn, my(q=rev(p)); if ((q>p) && isprime(q), listput(list, q-p));); Vec(list);} \\ Michel Marcus, Sep 07 2021

Python

from sympy import isprime, nextprime
def aupton(terms):
    alst, p = [], 2
    while len(alst) < terms:
        revp = int(str(p)[::-1])
        if p < revp and isprime(revp):
            alst.append(revp - p)
        p = nextprime(p)
    return alst
print(aupton(49)) # Michael S. Branicky, Sep 08 2021

Formula

a(n) = reverse(A109308(n)) - A109308(n).

Extensions

Better name and more terms from Jon E. Schoenfield, Aug 20 2021