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A083969 Numbers n such that 2.n.3.n.5.n.7.n.11 is prime (dot means concatenation). 5
4, 18, 33, 42, 43, 57, 73, 76, 78, 87, 91, 93, 97, 102, 112, 114, 120, 141, 151, 177, 186, 193, 196, 219, 261, 267, 276, 280, 300, 307, 318, 322, 342, 352, 364, 366, 402, 435, 438, 445, 457, 462, 468, 484, 511, 580, 582, 633, 646, 651, 679, 706, 745, 774, 783 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Michael S. Branicky, Table of n, a(n) for n = 1..10000

EXAMPLE

2.4.3.4.5.4.7.4.11 = 2434547411, which is prime. Hence 4 is in the sequence.

MATHEMATICA

v={}; Do[If[PrimeQ[FromDigits[Join[{2}, IntegerDigits[n], {3}, IntegerDigits[n], {5}, IntegerDigits[n], {7}, IntegerDigits[n], {1, 1}]]], v=Append[v, n]], {n, 1000}]; v

Select[Range[660], PrimeQ[FromDigits[Join[{2}, IntegerDigits[ # ], {3}, IntegerDigits[ # ], {5}, IntegerDigits[ # ], {7}, IntegerDigits[ # ], {1, 1}]]] &] (* Stefan Steinerberger, Jun 28 2007 *)

PROG

(Python)

from sympy import isprime

def aupton(terms):

  n, alst = 1, []

  while len(alst) < terms:

    s = str(n)

    t = int('2'+s+'3'+s+'5'+s+'7'+s+'11')

    if isprime(t): alst.append(n)

    n += 1

  return alst

print(aupton(55)) # Michael S. Branicky, Apr 18 2021

CROSSREFS

Cf. A083677, A032711, A092115, A092117.

Sequence in context: A337003 A095823 A092116 * A110621 A124978 A031081

Adjacent sequences:  A083966 A083967 A083968 * A083970 A083971 A083972

KEYWORD

base,easy,nonn

AUTHOR

Farideh Firoozbakht, Jun 19 2003

EXTENSIONS

Edited by Stefan Steinerberger, Jun 28 2007

Edited by N. J. A. Sloane, Sep 18 2008 at the suggestion of R. J. Mathar

STATUS

approved

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Last modified December 3 00:59 EST 2021. Contains 349445 sequences. (Running on oeis4.)