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A165500 Maximum length of arithmetic progression starting at n such that each term k has tau(k)=tau(n) 2
1, 2, 3, 2, 5, 3, 7, 4, 2, 5, 11, 3, 13, 7, 6, 2, 17, 3, 19, 5, 7, 11 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Implicitly, we require the difference d of the arithmetic progression to be positive.

a(n) <= n for all n.

LINKS

Table of n, a(n) for n=1..22.

EXAMPLE

For n=4, tau(n)=3 so each term of the arithmetic progression must be a prime square. The difference d must be odd for n+d to qualify, in which case n+2d is even and does not qualify; so a(4)=2 is an upper bound.

CROSSREFS

Cf. A165498, A165501, A088430.

Sequence in context: A081812 A139421 A219964 * A072505 A095163 A033677

Adjacent sequences:  A165497 A165498 A165499 * A165501 A165502 A165503

KEYWORD

hard,nonn,more

AUTHOR

Hugo van der Sanden, Sep 21 2009, Oct 09 2009

EXTENSIONS

Extended to n=22 taking advantage of A088430 for n=19, Hugo van der Sanden, Jun 02 2015

STATUS

approved

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Last modified July 26 18:16 EDT 2017. Contains 289839 sequences.