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A136626 For every number n in Ulam's spiral the sequence gives the number of primes around it (number n excluded). 15
4, 2, 3, 3, 2, 3, 2, 3, 3, 2, 3, 5, 3, 2, 2, 2, 2, 3, 3, 3, 3, 2, 2, 2, 1, 0, 2, 3, 3, 3, 2, 3, 3, 1, 2, 2, 2, 3, 3, 2, 2, 3, 2, 1, 1, 2, 2, 2, 1, 1, 1, 1, 1, 2, 3, 2, 2, 2, 1, 2, 1, 2, 2, 1, 3, 3, 2, 1, 2, 3, 4, 4, 3, 3, 2, 0, 1, 2, 1, 1, 1, 1, 0, 1, 2, 2, 2, 1, 1, 2, 1, 0, 2, 2, 4, 3, 2, 1, 0, 1, 0, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

In Ulam's lattice there are 8 numbers around any number.

LINKS

Table of n, a(n) for n=1..102.

EXAMPLE

Numbers around 13 are 3, 12, 29, 30, 31, 32, 33, 14 -> 3, 29, 31 are primes, so a(13)=3.

CROSSREFS

Cf. A063826, A115258, A136627.

Sequence in context: A345996 A190874 A307367 * A079623 A177864 A090112

Adjacent sequences:  A136623 A136624 A136625 * A136627 A136628 A136629

KEYWORD

easy,nonn

AUTHOR

Paolo P. Lava and Giorgio Balzarotti, Jan 14 2008

EXTENSIONS

Offset 1 per example and correction for a(32) by Kevin Ryde, Jul 04 2020

STATUS

approved

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Last modified May 21 06:36 EDT 2022. Contains 353889 sequences. (Running on oeis4.)