A109308 Lesser emirps (primes whose digit reversal is a larger prime).

13, 17, 37, 79, 107, 113, 149, 157, 167, 179, 199, 337, 347, 359, 389, 709, 739, 769, 1009, 1021, 1031, 1033, 1061, 1069, 1091, 1097, 1103, 1109, 1151, 1153, 1181, 1193, 1213, 1217, 1223, 1229, 1231, 1237, 1249, 1259, 1279, 1283, 1381, 1399, 1409, 1429

Offset: 1

Author

Zak Seidov, Jun 25 2005

Keywords

• base
• nonn

Links

• R. J. Mathar, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A006567 (emirps), A109309 (larger emirps).

Programs

Maple

read("transforms"):
A109308 := proc(n)
    option remember;
    local p,R ;
    if n = 1 then
        return 13 ;
    else
        p := nextprime(procname(n-1)) ;
        while true do
            R := digrev(p) ;
            if R> p and isprime(R) then
                return p;
            end if;
            p := nextprime(p) ;
        end do:
    end if;
end proc: # R. J. Mathar, Oct 12 2012

Mathematica

dr[n_]:=FromDigits[Reverse[IntegerDigits[n]]];Select[Prime[Range[1000]], PrimeQ[dr[ # ]]&&dr[ # ]>#&]

PARI

isok(p) = if (isprime(p), my(q=fromdigits(Vecrev(digits(p)))); (p < q) && isprime(q)); \\ Michel Marcus, Sep 07 2021

Python

from sympy import isprime, primerange
def ok(p): revp = int(str(p)[::-1]); return p < revp and isprime(revp)
print(list(filter(ok, primerange(1, 1430)))) # Michael S. Branicky, Sep 07 2021