A145709 Number of primes among first 10^n primes that have first and last digits both equal 1.
1, 6, 39, 393, 7737, 103788, 1230898, 13344414, 120133545, 1092391851
Offset: 1
Examples
a(1)=1 because among first 10^1 primes (i.e., from 2 to 29) there is just one prime with first and last digits equal 1, that is 11.
Programs
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UBASIC
10 'leading-trailing digits 20 N=11:C=4:Q=1 30 'print 2;3; 40 A=3:S=sqrt(N) 50 B=N\A 60 if B*A=N then 190 70 A=A+2 80 if A<=S then 50 90 R=str(N) 100 T=left(R,2):X=val(T) 110 U=right(R,1):Y=val(U) 120 if X=Y and X=1 then Aa=Aa+1 130 if X=Y and X=3 then Bb=Bb+1 140 if X=Y and X=7 then Cc=Cc+1 150 if X=Y and X=9 then Dd=Dd+1 160 C=C+1 170 'print C;N;X;Y;Aa;Bb;Cc;Dd 180 if C=10^Q then print C;N;Aa;Bb;Cc;Dd:Q=Q+1 190 N=N+2:goto 40
Extensions
Edited and two more terms added by Max Alekseyev, Sep 11 2009
a(9), a(10) from D. S. McNeil, Aug 29 2010