login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A252942 Smallest prime of the form "Concatenate(m,n,m)". 1
101, 313, 727, 131, 11411, 151, 13613, 373, 181, 191, 9109, 131113, 7127, 171317, 131413, 1151, 3163, 1171, 1181, 9199, 1201, 112111, 172217, 1231, 7247, 3253, 372637, 172717, 232823, 1291, 1301, 3313, 1321, 233323, 3343, 273527, 1361, 3373, 1381, 173917, 174017 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

LINKS

Danny Rorabaugh, Table of n, a(n) for n = 0..10000

EXAMPLE

111 is divisible by 3, and 212 is divisible by 2, but 313 is prime; therefore, a(1) = 313.

MAPLE

f:= proc(n) local dn, x, dx, p;

  dn:= 10^(1+ilog10(n));

  for x from 1 by 2 do if igcd(x, n) = 1 then

     dx:= 10^(1+ilog10(x));

     p:= x*(1+dx*dn)+n*dx;

     if isprime(p) then return(p) fi

  fi od

end proc:

101, seq(f(n), n=1..100); # Robert Israel, Apr 07 2015

# second Maple program:

a:= proc(n) local m, p; for m do

      p:= parse(cat(m, n, m));

      if isprime(p) then break fi od; p

    end:

seq(a(n), n=0..50);  # Alois P. Heinz, Mar 16 2020

MATHEMATICA

mnmPrimes = {}; f[m_, n_] := FromDigits[Flatten[{IntegerDigits[m], IntegerDigits[n], IntegerDigits[m]}]]; Do[m = 1; While[True, If[PrimeQ[f[m, n]], AppendTo[mnmPrimes, f[m, n]]; Break[]]; m+=2], {n, 0, 40}]; mnmPrimes

PROG

(PARI) a(n) = {m=1; while (! isprime(p=eval(concat(Str(m), concat(Str(n), Str(m))))), m+=2); p; } \\ Michel Marcus, Mar 23 2015

(Sage)

def A252942(n):

    m = 1

    sn = str(n)

    while True:

        sm = str(m)

        a = int(sm + sn + sm)

        if is_prime(a):

            return a

        m += 2

A252942(40) # Danny Rorabaugh, Mar 31 2015

(Haskell)

a252942 n = head [y | m <- [1..],

   let y = read (show m ++ show n ++ show m) :: Integer, a010051' y == 1]

-- Reinhard Zumkeller, Apr 08 2015

CROSSREFS

Cf. A090287, A256048.

Cf. A010051.

Sequence in context: A195294 A142578 A256048 * A090287 A134971 A082770

Adjacent sequences:  A252939 A252940 A252941 * A252943 A252944 A252945

KEYWORD

base,easy,nonn

AUTHOR

Ivan N. Ianakiev, Mar 23 2015

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 27 18:20 EST 2022. Contains 350611 sequences. (Running on oeis4.)