|
%I #18 Jun 21 2018 03:07:07
%S 23,37,53,73,113,137,173,193,233,293,313,373,4111,433,4723,5323,593,
%T 613,673,7129,733,797,8311,8923,977,1013,1033,10711,1093,11311,1277,
%U 13147,1373,13913,1493,15131,15731,1637,16729,1733,17911,18119,1913
%N a(n) = p.q in decimal notation where p = prime(n) and q is the smallest prime (A066065(n)) such that the concatenation p.q is a prime.
%H Harry J. Smith, <a href="/A066064/b066064.txt">Table of n, a(n) for n = 1..1000</a>
%e A000040(2) = 3 and as 32, 33 and 35 are composite, the next prime 7 = A066065(2) yields a(2) = 37.
%t Table[Block[{q = 3, d = IntegerDigits[p], k}, While[! PrimeQ@ Set[k, FromDigits[Join[d, IntegerDigits[q]]]], q = NextPrime@ q]; k], {p, Prime@ Range@ 43}] (* _Michael De Vlieger_, Jun 19 2018 *)
%o (PARI) digitsIn(x)= { local(d); if (x==0, return(1)); d=1 + log(x)\log(10); if (10^d == x, d++, if (10^(d-1) > x, d--)); return(d) }
%o Concat(a, b)= { return(a*10^digitsIn(b) + b) }
%o { for (n = 1, 1000, p=prime(n); q=2; while(!isprime(c=Concat(p, q)), q=nextprime(q + 1)); write("b066064.txt", n, " ", c) ) } \\ _Harry J. Smith_, Nov 09 2009
%K base,nonn
%O 1,1
%A _Reinhard Zumkeller_, Dec 01 2001
|
