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A065684

Number of primes <= prime(n) which begin with a 5.

0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 5, 6, 7, 8, 9, 10, 11

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,16

LINKS

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

EXAMPLE

a(i) = 1 for 2 < i < 16 and a(16) = 2 as 53 = A000040(16) is the second prime beginning with 5. a(664579) = 72951 (A000040(664579) = 9999991 is the largest prime < 10^7).

MATHEMATICA

Accumulate@ Array[Boole[First@ IntegerDigits@ Prime@ # == 5] &, 103] (* Michael De Vlieger, Jun 14 2018 *)

PROG

(PARI) lista(n) = { my(a=[p\10^logint(p, 10)==5 | p<-primes(n)]); for(i=2, #a, a[i]+=a[i-1]); a} \\ Harry J. Smith, Oct 26 2009

CROSSREFS

Cf. A000040, A045711, A065680.

Sequence in context: A244919 A158799 A157532 * A065683 A065682 A065681

Adjacent sequences: A065681 A065682 A065683 * A065685 A065686 A065687

KEYWORD

base,nonn

AUTHOR

Reinhard Zumkeller, Nov 13 2001

STATUS

approved

URL: https://oeis.org/A065684

⇱ A065684 - OEIS