The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A281158

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A281158

Least prime p such that n^2 + (n - p)^2 is prime.
(history; published version)

#22 by Charles R Greathouse IV at Wed Feb 01 13:53:34 EST 2017

STATUS

editing

approved

#21 by Charles R Greathouse IV at Wed Feb 01 13:53:32 EST 2017

PROG

(PARI) a(n) = {my(p=2); while (! isprime(n^2 + (n - p)^2), p = nextprime(p+1)); p; } \\ Michel Marcus, Jan 16 2017

STATUS

proposed

editing

#20 by Thomas Ordowski at Mon Jan 30 01:28:33 EST 2017

STATUS

editing

proposed

#19 by Robert G. Wilson v at Sun Jan 29 13:57:24 EST 2017

COMMENTS

First occurrence of p: 1, 2, 3, 16, 15, 29, 42, 74, 70, 69, 66, 107, 186, 188, 237, 324, 304, 358, 651, 961, 1499, 892, 1259, 804, 831, 1133, 754, 727, 2007, 2908, 2556, 3793, 956, 1502, 847, 3093, 4191, 6578, 13386, 8753, 3064, 6566, 17091, etc. Robert G. Wilson v, Jan 29 2017

#18 by Robert G. Wilson v at Sun Jan 29 13:44:18 EST 2017

LINKS

Robert G. Wilson v, <a href="/A281158/b281158.txt">Table of n, a(n) for n = 1..10000</a>

STATUS

proposed

editing

#17 by Michael De Vlieger at Sat Jan 21 11:54:41 EST 2017

STATUS

editing

proposed

#16 by Michael De Vlieger at Sat Jan 21 11:54:37 EST 2017

MATHEMATICA

Table[p = 2; While[! PrimeQ[n^2 + (n - p)^2], p = NextPrime@ p]; p, {n, 86}] (* Michael De Vlieger, Jan 21 2017 *)

STATUS

proposed

editing

#15 by Altug Alkan at Mon Jan 16 16:11:01 EST 2017

STATUS

editing

proposed

Discussion

Mon Jan 16

16:21

Michel Marcus: 15:00 discussion, actually the terms are not all the same; thanks Altug

Tue Jan 17

04:03

Altug Alkan: Thanks too, however this is interesting observation and it has a reason in my opinion, thank you very much, best regards.

04:11

Thomas Ordowski: A069002(76) = 15 composite.

#14 by Altug Alkan at Mon Jan 16 16:09:23 EST 2017

COMMENTS

Conjecture: such p a(n) < n for n > 3.

Discussion

Mon Jan 16

16:11

Altug Alkan: Thank you very much, I edited them. Best regards.

#13 by Altug Alkan at Mon Jan 16 15:51:41 EST 2017

DATA

2, 3, 5, 3, 3, 5, 5, 3, 5, 3, 5, 5, 3, 3, 11, 7, 5, 11, 3, 7, 11, 5, 3, 5, 3, 5, 5, 3, 13, 7, 5, 5, 5, 5, 11, 7, 5, 13, 5, 3, 7, 17, 3, 3, 7, 5, 17, 5, 3, 7, 11, 7, 3, 13, 13, 5, 5, 3, 5, 17, 5, 7, 5, 3, 3, 31, 7, 3, 29, 23, 5, 17, 11, 19, 11, 17, 5, 23, 5, 3, 7, 5, 5, 5, 7, 17, 5, 3, 13, 11, 17, 5, 11, 3, 3, 5, 7, 5, 5, 11

Discussion

Mon Jan 16

16:06

Michel Marcus: rather ? Conjecture: a(n) < n for n > 3.