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A197817 Smallest composite m such that m and the smallest prime divisor of m begin with n. 0
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Except for the number 22, the sequence A176597 (double primes: concatenation of the n-th prime with itself) is a subset 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: A079842 A014756 A014748 * A152144 A282344 A249627

Adjacent sequences:  A197814 A197815 A197816 * A197818 A197819 A197820

KEYWORD

nonn,base

AUTHOR

Michel Lagneau, Oct 18 2011

STATUS

approved

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Last modified February 23 18:13 EST 2019. Contains 320437 sequences. (Running on oeis4.)