

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
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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



