A089396 - OEIS

%I #9 Dec 23 2021 00:48:17

%S 1,12,106,1018,10312,105502,1197058,11056216

%N Smallest n-digit term of A089395.

%e a(3) = 256 which is the smallest 3-digit number such that 2*56 + 1 = 113, 25*6 + 1 = 151 and 256 + 1 = 257 are all prime.

%p with(combinat): ds:=proc(s) local j: RETURN(add(s[j]*10^(j-1),j=1..nops(s))):end: for d from 1 to 7 do sch:=[seq([1,op(i),d+1],i=[[],seq([j],j=2..d)])]: for n from 10^(d-1) to 10^d-1 do sn:=convert(n,base,10): fl:=0: for s in sch do m:=mul(j,j=[seq(ds(sn[s[i]..s[i+1]-1]),i=1..nops(s)-1)])+1: if not isprime(m) then fl:=1: break fi od: if fl=0 then printf("%d, ",n):break fi od od: # C. Ronaldo

%Y Cf. A089392, A089393, A089394, A089395, A089397.

%K base,nonn

%O 0,2

%A _Amarnath Murthy_, Nov 10 2003

%E Corrected and extended by C. Ronaldo (aga_new_ac(AT)hotmail.com), Dec 25 2004

%E One more term (a(7)) from _Harvey P. Dale_, Mar 23 2019