The OEIS is supported by the many generous donors to the OEIS Foundation.

 Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A145710 Number of primes among first 10^n primes that have first and last digits both equal 3 (not counting the prime 3). 3

%I

%S 0,4,32,278,2250,18839,162662,1433999,12811208,115798814

%N Number of primes among first 10^n primes that have first and last digits both equal 3 (not counting the prime 3).

%e 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.

%o (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

%Y A145709 A145711 A145712 A145713

%K more,nonn,base

%O 1,2

%A _Enoch Haga_, Oct 16 2008

%E Edited and two more terms added by _Max Alekseyev_, Sep 11 2009

%E a(9), a(10) from _D. S. McNeil_, Aug 29 2010

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 7 17:25 EST 2022. Contains 358668 sequences. (Running on oeis4.)