login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A178668 Maximal prime divisor of the average of the twin prime pairs, different from 2 and 3. In case of maximal prime divisor is 2 or 3, then a(n)=1. 0
1, 1, 1, 1, 5, 7, 5, 1, 17, 1, 23, 5, 5, 1, 11, 19, 5, 5, 47, 13, 29, 7, 1, 11, 29, 19, 5, 103, 107, 11, 5, 137, 23, 13, 7, 17, 43, 7, 59, 13, 1, 41, 71, 43, 31, 11, 17, 11, 19, 31, 67, 5, 139, 283, 41, 149, 13, 313, 23, 13, 37, 13, 347, 29, 11, 71, 17, 373, 7, 11, 13, 397, 17, 1, 443, 7, 113, 13, 31, 467, 11, 5, 13, 11, 271, 181, 11, 37, 7, 281, 113, 577, 17, 7, 59, 593, 199, 17, 157, 13 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

COMMENTS

78 from the first 100 terms are first or second members of twin pairs and only 12 are not. In a natural supposition that for large prime terms the latter should be in the majority, there are reasons to assume that the number N for which it occurs for the first time is very large.

The average of a twin-prime pair is the same as 1 + the lower twin prime, whose largest prime factor is tabulated in A060210.

LINKS

Table of n, a(n) for n=1..100.

MATHEMATICA

s = Plus @@@ Select[ Partition[ Prime@ Range@ 350, 2, 1], #[[1]] + 2 == #[[2]] &]; f[n_] := Max[First /@ FactorInteger@ n] /. {2 -> 1, 3 -> 1}, f /@ s

CROSSREFS

Cf. A178456, A178527, A001359

Sequence in context: A002338 A226021 A242059 * A198744 A201944 A165242

Adjacent sequences:  A178665 A178666 A178667 * A178669 A178670 A178671

KEYWORD

nonn

AUTHOR

Vladimir Shevelev, Dec 25 2010

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified October 22 02:06 EDT 2017. Contains 293756 sequences.