A145710 Number of primes among first 10^n primes that have first and last digits both equal 3 (not counting the prime 3).

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

Offset

1,2

Links

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

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

Crossrefs

A145709 A145711 A145712 A145713

Sequence in context: A065089 A113329 A246818 * A264633 A319183 A199566

Adjacent sequences: A145707 A145708 A145709 * A145711 A145712 A145713

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