A136627 For every number n in Ulam's spiral the sequence gives the number of primes around it (number n included).

4, 3, 4, 3, 3, 3, 3, 3, 3, 2, 4, 5, 4, 2, 2, 2, 3, 3, 4, 3, 3, 2, 3, 2, 1, 0, 2, 3, 4, 3, 3, 3, 3, 1, 2, 2, 3, 3, 3, 2, 3, 3, 3, 1, 1, 2, 3, 2, 1, 1, 1, 1, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 2, 1, 3, 3, 3, 1, 2, 3, 5, 4, 4, 3, 2, 0, 1, 2, 2, 1, 1, 1, 1, 1, 2, 2, 2, 1, 2, 2, 1, 0, 2, 2, 4, 3, 3, 1, 0, 1, 1, 2

Offset

1,1

Comments

In Ulam's lattice there are 8 numbers around any number. The sequence is similar to A136626 with an increment of 1 for any prime position.

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 and 13 itself are primes, so a(13)=4.

Crossrefs

Cf. A063826, A115258, A136626.

Sequence in context: A238234 A367439 A367126 * A108171 A231475 A106055

Adjacent sequences: A136624 A136625 A136626 * A136628 A136629 A136630

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