A267134 - OEIS

A267134

a(n) = n minus the number of primes of form 6m + 1 that are less than n-th prime of form 6m - 1.

1, 1, 1, 1, 2, 1, 1, 2, 3, 2, 1, 2, 2, 2, 2, 2, 3, 3, 1, 2, 3, 3, 3, 1, 1, 2, 2, 3, 4, 5, 4, 4, 4, 4, 3, 3, 4, 2, 3, 3, 3, 3, 2, 3, 3, 3, 4, 4, 4, 5, 6, 4, 5, 6, 5, 6, 7, 5, 4, 4, 5, 6, 5, 6, 6, 6, 4, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5, 6, 6, 7, 8, 6, 7, 7, 6, 6, 4, 4, 5, 6, 4, 4, 4, 5, 6

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OFFSET

1,5

LINKS

Table of n, a(n) for n=1..100.

EXAMPLE

a(5) = 2 because the fifth prime of the form 6m - 1 is 29, there are three primes of the form 6m + 1 less than 29 (namely 7, 13, 19) and 5 - 3 = 2.

MATHEMATICA

s = Prime@Range@120 /. p_ /; Mod[p, 6] != 5 -> Nothing; Table[n - Count[Flatten@ Prime@ Range@ PrimePi@ Take[s, {n}], p_ /; Mod[p, 6] == 1], {n, 120}] (* Michael De Vlieger, Feb 10 2016 *)

CROSSREFS

Cf. A002476, A007528.

Sequence in context: A165475 A341456 A319420 * A098280 A005793 A183391

Adjacent sequences: A267131 A267132 A267133 * A267135 A267136 A267137

KEYWORD

sign

AUTHOR

Gionata Neri, Jan 10 2016

STATUS

approved