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Search: id:A109744
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| A109744 |
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Least multiple of n such that every partial concatenation followed by a 7 is prime. |
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+0
2
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| 1, 2, 3, 4, 5, 12, 42, 48, 9, 90, 22, 96, 299, 154, 60, 288, 918, 1026, 380, 60, 2184, 616, 23, 120, 175, 2964, 135, 980, 319, 1230, 2015, 2464, 1056, 272, 2310, 2448, 111, 11628, 2301, 8800, 7134, 252, 4730, 3036, 1665, 3634, 1551, 2016, 147, 4950
(list; graph; listen)
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OFFSET
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1,2
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EXAMPLE
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17,127,1237,12347,123457,... etc. are all prime.
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MAPLE
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Lcat := proc(L) local a, i; a := 0 ; for i from 1 to nops(L) do a := a*10^(max(1, ilog10(op(i, L))+1))+op(i, L) ; od: RETURN(a) ; end: A109744 := proc(nmax) local a, k, n; a := [1] ; while nops(a) < nmax do n := nops(a)+1 ; k := 1; while not isprime(Lcat([op(a), k*n, 7]) ) do k := k+1 ; od ; a := [op(a), k*n] ; od: RETURN(a) ; end: op(A109744(50)) ; - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Aug 15 2007
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CROSSREFS
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Cf. A110436, A110437.
Adjacent sequences: A109741 A109742 A109743 this_sequence A109745 A109746 A109747
Sequence in context: A069469 A109849 A007662 this_sequence A065635 A101546 A026471
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KEYWORD
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base,nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Aug 03 2005
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EXTENSIONS
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More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Aug 15 2007
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