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A082612 Numbers n such that ((n-1)^2+1)/2 and n^2+1 and ((n+1)^2+1)/2 are prime if n is even or (n-1)^2+1 and (n^2+1)/2 and (n+1)^2+1 are prime if n is odd. 5
3, 4, 5, 10, 15, 25, 170, 205, 570, 715, 780, 950, 1095, 1315, 1420, 1615, 2055, 2380, 2405, 2730, 2925, 3755, 3850, 4120, 4300, 4615, 4795, 5015, 5055, 5475, 5850, 6360, 6460, 6785, 6800, 6970, 7100, 7240, 7855, 8115, 8175, 8720, 9425, 9475, 9630, 10150 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

I believe this is an infinite sequence, though a proof seems to be still far off. 155th term is 62910. There are probably infinitely many consecutive n^2+1 or (n^2+1)/2 primes. That is, n^2+1 and (n+2)^2+1 or (n^2+1)/2 and ((n+2)^2+1)/2 are both prime infinitely often.

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

EXAMPLE

a(4)=10 (9^2+1)/2=41 and 10^2+1=101 and (11^2+1)/2=61 are prime.

MATHEMATICA

neoQ[n_]:=If[EvenQ[n], AllTrue[{((n-1)^2+1)/2, n^2+1, ((n+1)^2+1)/2}, PrimeQ], AllTrue[{(n-1)^2+1, (n^2+1)/2, (n+1)^2+1}, PrimeQ]]; Select[Range[ 6400], neoQ] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Mar 19 2018 *)

CROSSREFS

Sequence in context: A183050 A176848 A058615 * A339569 A170926 A122413

Adjacent sequences:  A082609 A082610 A082611 * A082613 A082614 A082615

KEYWORD

nonn

AUTHOR

Robin Garcia, Sep 23 2004

EXTENSIONS

More terms from Harvey P. Dale, Mar 19 2018

STATUS

approved

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Last modified September 19 00:22 EDT 2021. Contains 347549 sequences. (Running on oeis4.)