This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A068876 Smallest n-digit prime with property that digits alternate in parity. 7
 2, 23, 101, 2129, 10103, 210101, 1010129, 21010127, 101010167, 2101010147, 10101010163, 210101010187, 1010101010341, 21010101010147, 101010101010323, 2101010101010141, 10101010101010141, 210101010101010323, 1010101010101010143 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Robert Israel, Table of n, a(n) for n = 1..700 EXAMPLE a(4) = 2129 as 2, 1, 2 and 9 have even and odd parity alternately. MAPLE alp:= proc(n) local L, d; L:= convert(n, base, 10); d:= nops(L); if d::even then L:= L + map(op, [[0, 1]\$(d/2)]) else L:= L + map(op, [[0, 1]\$((d-1)/2), [0]]) fi; nops(convert(L mod 2, set))=1 end proc: f:= proc(d) local s;   if d::even then s:= 2*10^(d-1)+(10^d-1)/99-1   else s:= (10^(d+1)-1)/99-1   fi;   do s:= nextprime(s);      if alp(s) then return s fi   od end proc: seq(f(d), d=1..20); # Robert Israel, Aug 14 2018 MATHEMATICA fQ[n_] := Block[{m = Mod[ IntegerDigits@ n, 2]}, m == Split[m, UnsameQ][[1]]]; f[n_] := Block[{c = 1 + 100 (100^Ceiling[n/2 - 1] - 1)/99, k}, k = If[ OddQ@ n, c, 2*10^(n - 1) + c]; k = NextPrime[k - 1]; While[ !fQ@ k, k = NextPrime@ k]; k]; Array[f, 21] (* Robert G. Wilson v, Apr 01 2011 *) PROG (Sage) concat = lambda x: Integer(''.join(map(str, x)), base=10) def A068876(n): ....dd = {0:range(0, 10, 2), 1: range(1, 10, 2)} ....for d0 in [1..9]: ........if n % 2 == 0 and d0 % 2 == 1: continue # optimization ........ds = [dd[(d0+1+i) % 2] for i in range(n-1)] ........for dr in CartesianProduct(*ds): ............c = concat([d0]+dr) ............if is_prime(c): return c  # D. S. McNeil, Apr 02 2011 CROSSREFS Cf. A030144, A068877, A056830. Sequence in context: A053999 A131176 A141405 * A073175 A141888 A285811 Adjacent sequences:  A068873 A068874 A068875 * A068877 A068878 A068879 KEYWORD nonn,base AUTHOR Amarnath Murthy, Mar 19 2002 EXTENSIONS a(9)-a(13) corrected and a(14)-a(19) from Donovan Johnson, Apr 01 2011 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 17 09:05 EDT 2019. Contains 327128 sequences. (Running on oeis4.)