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A065685
Number of primes <= prime(n) which begin with a 6.
2
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2
OFFSET
1,19
LINKS
EXAMPLE
a(17) = 0, a(18) = 1: 61 = A000040(18) is the first prime beginning with 6. a(664579) = 72257 (A000040(664579) = 9999991 is the largest prime < 10^7).
MATHEMATICA
Accumulate@ Array[Boole[First@ IntegerDigits@ Prime@ # == 6] &, 105] (* Michael De Vlieger, Jun 14 2018 *)
PROG
(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) == 6, a++); p=nextprime(p+1)); write("b065685.txt", n, " ", a) ) } \\ Harry J. Smith, Oct 26 2009
CROSSREFS
Sequence in context: A065687 A300403 A077433 * A084100 A329683 A130130
KEYWORD
base,nonn
AUTHOR
Reinhard Zumkeller, Nov 13 2001
STATUS
approved