A090266 Least k such that concatenation k, prime(n), k is a prime.

7, 1, 1, 3, 13, 17, 1, 9, 1, 1, 3, 3, 3, 3, 1, 1, 3, 3, 3, 7, 3, 3, 1, 57, 17, 3, 3, 1, 9, 1, 33, 1, 19, 3, 1, 3, 3, 9, 57, 1, 3, 21, 7, 9, 1, 21, 9, 3, 7, 21, 7, 1, 3, 1, 3, 3, 3, 3, 9, 7, 3, 3, 3, 3, 9, 1, 9, 41, 7, 3, 3, 1, 29, 9, 11, 1, 3, 9, 1, 9, 7, 3, 3, 17, 9, 1, 31, 17, 3, 17, 3, 7, 27, 3, 9, 1

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Mathematica

lk[n_]:=Module[{idn=IntegerDigits[n], k=1}, While[!PrimeQ[FromDigits[ Join[ IntegerDigits[k], idn, IntegerDigits[k]]]], k=k+2]; k]; Table[lk[i], {i, Prime[ Range[100]]}] (* Harvey P. Dale, Apr 26 2015 *)

Prog

(Python)
from sympy import prime, isprime
def a(n):
    spn = str(prime(n)); k = 1; sk = str(k)
    while not isprime(int(sk + spn + sk)): k += 1; sk = str(k)
    return k
print([a(n) for n in range(1, 97)]) # Michael S. Branicky, Jul 01 2021

Crossrefs

Cf. A090267, A090269.

Sequence in context: A241299 A090269 A086867 * A010142 A294646 A051422

Adjacent sequences: A090263 A090264 A090265 * A090267 A090268 A090269

Keyword

base,nonn

Author

Amarnath Murthy, Nov 28 2003

Extensions

More terms from David Wasserman, Oct 24 2005

Status

approved