

A145713


Number of primes p in the range 9 < p <= prime(10^n) that begin and end with the same digit.


4




OFFSET

1,2


LINKS

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


FORMULA

a(n) = A145709(n) + A145710(n) + A145711(n) + A145712(n). [R. J. Mathar, Aug 02 2010]


EXAMPLE

The initial 1 is from the prime 11.
a(4)=1180 because to 10^4 or 10000 primes, ending in 104729=A006988(4), there are 1180 primes with equal and distinct first and last digits: 1 and 1, 3 and 3, 7 and 7 and 9 and 9.


CROSSREFS

Cf. A145709  A145712
Sequence in context: A068767 A233830 A046715 * A123512 A079515 A024131
Adjacent sequences: A145710 A145711 A145712 * A145714 A145715 A145716


KEYWORD

hard,more,nonn,base


AUTHOR

Enoch Haga, Oct 16 2008


EXTENSIONS

Edited by N. J. A. Sloane, Aug 16 2010
a(6) corrected and a(7)a(10) added by D. S. McNeil, Aug 29 2010


STATUS

approved



