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 A090871 Numbers k such that the six numbers 1.prime(k).prime(k+1), prime(k).1.prime(k+1), prime(k).prime(k+1).1, 1.prime(k-1).prime(k), prime(k-1).1.prime(k) and prime(k-1).prime(k).1, where "." denotes concatenation, are primes. 0
 589407, 2372675, 5609052, 5698663, 12353466, 12534100, 14155932, 24208353, 25303609, 30939821, 32915465, 36240880, 37168122, 50679993, 52677223, 60090497, 66071478, 67690661, 75747212, 88096704, 89077730, 98871534, 115631955, 119515953, 127817446, 134262693 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..26. EXAMPLE 5698663 is a term because prime(5698662)=98842171, prime(5698663)=98842223 and prime(5698664)=98842231 and the six numbers 19884217198842223, 98842171198842223, 98842171988422231, 19884222398842231, 98842223198842231 and 98842223988422311 are primes. MATHEMATICA v={}; Do[If[PrimeQ[FromDigits[Join[{1}, IntegerDigits[Prime[k-1]], IntegerDigits [Prime[k]]]]]&&PrimeQ[FromDigits[Join[IntegerDigits[Prime[k-1]], {1}, IntegerDigits[Prime[k]]]]]&&PrimeQ[FromDigits[Join[IntegerDigits [Prime[k-1]], IntegerDigits[Prime[k]], {1}]]]&& PrimeQ[FromDigits [Join[{1}, IntegerDigits[Prime[k]], IntegerDigits[Prime[k+1]]]]] &&PrimeQ[FromDigits[Join[IntegerDigits[Prime[k]], {1}, IntegerDigits[ Prime[k+1]]]]]&& PrimeQ[FromDigits[Join[IntegerDigits[Prime[k]], IntegerDigits[Prime[k+1]], {1}]]], v=Append[v, k]; Print[v]], {k, 2, 3*10^7}]; v CROSSREFS Sequence in context: A206222 A202160 A216927 * A237493 A232361 A236736 Adjacent sequences: A090868 A090869 A090870 * A090872 A090873 A090874 KEYWORD nonn,base AUTHOR Farideh Firoozbakht, Jan 25 2004 EXTENSIONS a(9) and beyond from Michael S. Branicky, Mar 21 2023 STATUS approved

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Last modified August 10 19:25 EDT 2024. Contains 375058 sequences. (Running on oeis4.)