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 A145709 Number of primes among first 10^n primes that have first and last digits both equal 1. 4
 1, 6, 39, 393, 7737, 103788, 1230898, 13344414, 120133545, 1092391851 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS EXAMPLE 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. PROG (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 CROSSREFS Sequence in context: A352839 A006678 A252761 * A280006 A336291 A034661 Adjacent sequences: A145706 A145707 A145708 * A145710 A145711 A145712 KEYWORD more,nonn,base AUTHOR Enoch Haga, Oct 16 2008 EXTENSIONS Edited and two more terms added by Max Alekseyev, Sep 11 2009 a(9), a(10) from D. S. McNeil, Aug 29 2010 STATUS approved

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Last modified December 6 09:26 EST 2022. Contains 358608 sequences. (Running on oeis4.)