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A145710
Number of primes among first 10^n primes that have first and last digits both equal 3 (not counting the prime 3).
3
0, 4, 32, 278, 2250, 18839, 162662, 1433999, 12811208, 115798814
OFFSET
1,2
EXAMPLE
a(2)= 4 because among first 10^2 primes (i.e., from 2 to 541), there are 4 primes with first and last digits equal 3, that are 313, 353, 373, and 383.
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
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