|
Search: id:A065686
|
|
|
| A065686 |
|
Number of primes <= prime(n) which begin with a 7. |
|
+0
2
|
|
| 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
(list; graph; listen)
|
|
|
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 < 10,000,000).
|
|
PROGRAM
|
(PARI) digitsIn(x)= { local(d); if (x==0, return(1)); d=1 + log(x)\log(10); if (10^d == x, d++, if (10^(d-1) > x, d--)); return(d) } MSD(x)= { return(x\10^(digitsIn(x)-1)) } { a=0; p=2; for (n=1, 1000, q=prime(n); while (p <= q, if(MSD(p) == 7, a++); p=nextprime(p+1)); write("b065686.txt", n, " ", a) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Oct 26 2009]
|
|
CROSSREFS
|
A065680, A000040.
Sequence in context: A005102 A030241 A062750 this_sequence A158411 A065680 A093391
Adjacent sequences: A065683 A065684 A065685 this_sequence A065687 A065688 A065689
|
|
KEYWORD
|
base,nonn
|
|
AUTHOR
|
Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Nov 13 2001
|
|
|
Search completed in 0.002 seconds
|
