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A083966
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Numbers n such that the concatenation 2n3n5n7 is prime.
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4
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1, 6, 8, 9, 16, 17, 18, 21, 23, 24, 29, 32, 39, 64, 70, 78, 84, 85, 98, 1000, 1005, 1013, 1033, 1038, 1041, 1047, 1056, 1065, 1066, 1076, 1087, 1091, 1102, 1107, 1109, 1115, 1118, 1121, 1137, 1139, 1152, 1156, 1164, 1167, 1171, 1173, 1185, 1199, 1220, 1241
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Numbers n such that the concatenation of 2, n, 3, n, 5, n and 7 is prime.
This concatenation is fp(4, n) as defined in A083677.
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EXAMPLE
| 8 and 21 are in the sequence because 2838587 and 2213215217 are primes.
16 is in the sequence because 2163165167 is prime. For any 3-digit number n, fp(4, n) is divisible by 7, so there are no 3-digit numbers in the sequence.
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MAPLE
| v={}; Do[If[PrimeQ[FromDigits[Join[{2}, IntegerDigits[n], {3}, IntegerDigits[n], {5}, IntegerDigits[n], {7}]]], v=Append[v, n]], {n, 1300}]; v
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CROSSREFS
| Cf. A032711, A083677, A083969, A092117.
Sequence in context: A085725 A049721 A092115 * A074326 A174213 A099102
Adjacent sequences: A083963 A083964 A083965 * A083967 A083968 A083969
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KEYWORD
| base,easy,nonn
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AUTHOR
| Farideh Firoozbakht (f.firoozbakht(AT)sci.ui.ac.ir), Jun 15 2003, Jun 19 2003
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EXTENSIONS
| Edited and extended by David Wasserman (wasserma(AT)spawar.navy.mil), Dec 06 2004
Edited by N. J. A. Sloane (njas(AT)research.att.com) at the suggestion of Andrew Plewe, May 31 2007
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