A068660 Primes formed from the concatenation of k, k+1 and k for some k.

787, 9109, 111211, 131413, 333433, 373837, 394039, 414241, 474847, 575857, 596059, 616261, 697069, 717271, 777877, 798079, 818281, 838483, 101102101, 103104103, 129130129, 149150149, 181182181, 187188187, 189190189, 191192191, 193194193, 207208207, 217218217

Offset

1,1

Links

Michael S. Branicky, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Harvey P. Dale)

Maple

ncat:= (a, b) -> a*10^(1+ilog10(b))+b:
select(isprime, [seq(ncat(n, ncat(n+1, n)), n=1..1000, 2)]); # Robert Israel, Oct 23 2015

Mathematica

concat[n_]:=Module[{idn=IntegerDigits[n]}, FromDigits[Join[idn, IntegerDigits[ n+1], idn]]]; Select[concat/@Range[200], PrimeQ] (* Harvey P. Dale, Aug 20 2014 *)
A = Table[(n*10^(Floor[Log[10, 10(n+1)]])+(n+1))*10^(Floor[Log[10, 10(n)]])+n, {n, 1, 120}]; Select[A, PrimeQ] (* José de Jesús Camacho Medina, Sep 09 2015 *)
Select[Table[FromDigits[Join[Flatten[IntegerDigits[{n, n + 1, n}]]]], {n, 200}], PrimeQ] (* Vincenzo Librandi, Sep 28 2015 *)

Prog

(Magma) [m: n in [2..300] | IsPrime(m) where m is Seqint(Intseq(n) cat Intseq(n+1) cat Intseq(n))]; // Vincenzo Librandi, Sep 28 2015
(PARI) for(n=1, 1e3, if(isprime(k=eval(Str(n, n+1, n))), print1(k", "))) \\ Altug Alkan, Sep 28 2015
(Python)
from sympy import isprime
def aupto(N):
  return [t for t in (int(str(k)+str(k+1)+str(k)) for k in range(1, N+1, 2)) if isprime(t)]
print(aupto(217)) # Michael S. Branicky, Jul 09 2021

Crossrefs

Cf. A068659, A262205.

These are the primes in A261618. - M. F. Hasler, Nov 25 2015

Sequence in context: A031896 A045231 A267476 * A097775 A321210 A072730

Adjacent sequences: A068657 A068658 A068659 * A068661 A068662 A068663

Keyword

base,nonn

Author

Amarnath Murthy, Mar 01 2002

Status

approved