

A145709


Number of primes among first 10^n primes that have first and last digits both equal 1.


4




OFFSET

1,2


LINKS

Table of n, a(n) for n=1..10.


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 'leadingtrailing 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

A145710, A145711, A145712, A145713
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



