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Search: id:A145709
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| A145709 |
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Number of primes among first 10^n primes that have first and last digits both equal 1. |
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+0
5
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OFFSET
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1,2
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EXAMPLE
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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.
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PROGRAM
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(Other) 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
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CROSSREFS
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A145710, A145711, A145712, A145713
Sequence in context: A031972 A124577 A006678 this_sequence A034661 A094654 A145001
Adjacent sequences: A145706 A145707 A145708 this_sequence A145710 A145711 A145712
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KEYWORD
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more,nonn,base
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AUTHOR
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Enoch Haga (Enokh(AT)comcast.net), Oct 16 2008
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EXTENSIONS
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Edited and two more terms added by Max Alekseyev (maxale(AT)gmail.com), Sep 11 2009
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