0,2

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.

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)

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

Sequence in context: A027142 A090816 A144133 this_sequence A166755 A154671 A037972

Adjacent sequences: A089393 A089394 A089395 this_sequence A089397 A089398 A089399

base,nonn

Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Nov 10 2003

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