A109744 Least multiple of n such that every partial concatenation followed by a 7 is prime.

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

Offset

1,2

Links

Table of n, a(n) for n=1..50.

Example

17, 127, 1237, 12347, 123457, ... etc. are all prime.

Maple

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, Aug 15 2007

Crossrefs

Cf. A110436, A110437.

Sequence in context: A069469 A175807 A165303 * A065635 A325693 A367140

Adjacent sequences: A109741 A109742 A109743 * A109745 A109746 A109747

Keyword

base,nonn

Author

Amarnath Murthy, Aug 03 2005

Extensions

More terms from R. J. Mathar, Aug 15 2007

Status

approved