A071256 Smallest multiple of n sandwiched between twin primes.

4, 4, 6, 4, 30, 6, 42, 72, 18, 30, 198, 12, 312, 42, 30, 192, 102, 18, 228, 60, 42, 198, 138, 72, 150, 312, 108, 420, 348, 30, 1302, 192, 198, 102, 420, 72, 1998, 228, 312, 240, 1230, 42, 1032, 660, 180, 138, 282, 192, 882, 150, 102, 312, 6360, 108, 660

Offset: 1

Author

Amarnath Murthy, May 22 2002

Keywords

• nice
• nonn
• changed

Comments

Conjecture: lim sup n ->infinity a(n)/n^2 exists = C, where 0Benoit Cloitre, May 23 2002

Links

• T. D. Noe, Table of n, a(n) for n=1..1000

Crossrefs

Cf. A071558.

Programs

Mathematica

Table[ s = 2; While[ Mod[s, n] + 2 - Boole[ PrimeQ[s - 1]] - Boole[ PrimeQ[s + 1]] > 0, s++]; s, {n, 1, 55}] (* Jean-François Alcover, Dec 08 2011, after Pari *)
With[{tpm=Mean/@Select[Partition[Prime[Range[1000]],2,1],#[[2]]-#[[1]] == 2&]},Flatten[Table[Select[tpm,Divisible[#,n]&,1],{n,60}]]] (* Harvey P. Dale, Apr 12 2012 *)

PARI

a(n) = my(s=2); while(s%n+2-isprime(s-1)-isprime(s+1)>0, s++); s;

Formula

a(n) = n*A071558(n). - Michel Marcus, Aug 29 2025

Extensions

More terms from Benoit Cloitre, May 23 2002