A065686 Number of primes <= prime(n) which begin with a 7.

0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4

Offset

1,20

Links

Harry J. Smith, Table of n, a(n) for n = 1..1000

Example

a(3) = 0, a(4) = 1. a(664579) = 71564 (A000040(664579) = 9999991 is the largest prime < 10^7).

Prog

(PARI) lista(n) = { my(a=[p\10^logint(p, 10)==7 | p<-primes(n)]); for(i=2, #a, a[i]+=a[i-1]); a} \\ Harry J. Smith, Oct 26 2009

Crossrefs

Cf. A000040, A045713, A065680.

Sequence in context: A062750 A368420 A193669 * A158411 A065680 A093391

Adjacent sequences: A065683 A065684 A065685 * A065687 A065688 A065689

Keyword

base,nonn,changed

Author

Reinhard Zumkeller, Nov 13 2001

Status

approved