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A175897 Numbers n with property that n*prime(n)+(n+1)*prime(n+1) is a perfect square s^2. 1
1681, 3146, 5917, 308950, 10553441, 10553550, 4273262954, 9781980985 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Or, numbers n with property that A033286(n)+A033286(n+1) is a perfect square s^2, A033286(n)=n*(n-th prime). [From Zak Seidov, Oct 12 2010]
a(9) > pi(4*10^12). [From Donovan Johnson, Oct 22 2010]
LINKS
EXAMPLE
{n,s}: {1681,6943},{3146,13487},{5917,26299},{308950,1647737}, {10553441,63320647},{10553550,63321299}; no more n's up to 2*10^8.
MATHEMATICA
Position[Total/@Partition[Table[n Prime[n], {n, 310000}], 2, 1], _? (IntegerQ[ Sqrt[#]]&)]//Flatten (* The program generates the first four terms of the sequence. To generate more, Increase the Range constant, but the program may take a long time to run. *) (* Harvey P. Dale, Feb 05 2022 *)
PROG
(PARI) isok(n) = issquare(n*prime(n)+(n+1)*prime(n+1)); \\ Michel Marcus, Oct 19 2013
CROSSREFS
Sequence in context: A221204 A145292 A228183 * A370355 A361705 A322745
KEYWORD
more,nonn
AUTHOR
Zak Seidov, Oct 11 2010
EXTENSIONS
a(7)-a(8) from Donovan Johnson, Oct 22 2010
STATUS
approved

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Last modified March 2 01:29 EST 2024. Contains 370447 sequences. (Running on oeis4.)