A197817 Smallest composite m such that m and the smallest prime divisor of m begin with n.

121, 20, 33, 4141, 55, 6161, 77, 8051, 9409, 10201, 1111, 120269, 1313, 140209, 150547, 160229, 1717, 180457, 1919, 20002379, 210367, 220417, 2323, 240277, 250247, 260123, 270187, 280157, 2929, 301781, 3131, 32003357, 330007, 340973, 350743, 360761, 3737, 380053

Offset

1,1

Comments

Except for the number 22, the sequence A176597 (double primes: concatenation of the n-th prime with itself) is a subsequence of this sequence.

Links

Table of n, a(n) for n=1..38.

Example

a(8) = 8051 = 83*97 => 8051 and 83 start with 8.

Maple

with(numtheory): for n from 1 to 60 do: l1:=length(n):i:=0:for m from 2 to 32*10^6 while(i=0) do: x:=factorset(m):y:=x[1]: l2:=length(m):x1:=floor(m/(10^(l2-l1))): l3:=length(y):x2:=floor(y/(10^(l3-l1))):if x1=n and x2=n and l2>=l1 and l3 >=l1 and type(m, prime)=false then i:=1: printf ( "%d %d \n", n, m):else fi :od:od:

Crossrefs

Cf. A176597, A197816.

Sequence in context: A014756 A014748 A334058 * A152144 A282344 A249627

Adjacent sequences: A197814 A197815 A197816 * A197818 A197819 A197820

Keyword

nonn,base

Author

Michel Lagneau, Oct 18 2011

Status

approved