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A048198 Number of primes between successive n's, where n mod 10 = 5. 4
2, 3, 3, 2, 3, 2, 2, 3, 2, 1, 3, 3, 0, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 3, 2, 1, 2, 2, 3, 1, 0, 3, 1, 1, 1, 3, 1, 2, 2, 1, 2, 1, 2, 2, 2, 1, 3, 1, 1, 2, 2, 1, 2, 0, 1, 1, 2, 2, 1, 2, 2, 2, 2, 1, 2, 2, 2, 1, 2, 1, 1, 1, 1, 2, 2, 1, 2, 2, 0, 1, 1, 2, 2, 2, 1, 1, 3, 0, 3, 1, 0, 2, 1, 1, 2, 2, 0, 2, 2, 1, 1, 2, 2, 2, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

A way to visualize the distribution of primes without the clutter of the numbers themselves. Consecutive 0's indicate stretches where there are no primes. Other patterns become obvious, as a string of 2's or 1's.

LINKS

Robert Israel, Table of n, a(n) for n = 0..10000

FORMULA

Starting at 0, count primes between 0-5, 5-15, 15-25, etc.

EXAMPLE

Between n's 115 and 125 there are no primes, indicated by the entry 0.

MAPLE

f:= n -> nops(select(isprime, [$10*n-4..10*n+4])):

map(f, [$0..100]); # Robert Israel, Nov 22 2018

MATHEMATICA

a[n_] := Length[Select[Range[Max[10 n - 4, 1], 10 n + 4], PrimeQ]]; Array[a, 100, 0] (* Amiram Eldar, Nov 22 2018 *)

PROG

(PARI) a(n) = my(na = 10*n - 5); my(nb = na + 10); primepi(nb - 1) - primepi(na + 1); \\ Michel Marcus, Aug 25 2013

CROSSREFS

Cf. A048199.

Sequence in context: A213512 A218774 A270824 * A096006 A182128 A131294

Adjacent sequences:  A048195 A048196 A048197 * A048199 A048200 A048201

KEYWORD

easy,nonn

AUTHOR

Enoch Haga

STATUS

approved

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Last modified May 29 05:00 EDT 2022. Contains 354122 sequences. (Running on oeis4.)