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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.)