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A090783 a(n) can be expressed as the difference of the squares of consecutive primes in just three distinct ways. 5
1848, 6888, 14280, 16008, 19152, 36120, 112728, 116832, 129480, 139080, 176520, 190632, 190968, 199752, 216840, 236208, 252120, 274848, 303960, 314160, 340368, 363720, 435792, 458280, 503160, 513240, 686160, 688680, 698880, 712680, 721560 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Giovanni Resta, Table of n, a(n) for n = 1..10000 (first 3091 terms from Robert Israel)

EXAMPLE

1848 = 463^2 - 461^2 = 233^2 - 229^2 = 157^2 - 151^2.

MAPLE

N:= 10^6: # to get all terms <= N

V:= Vector(N/4):

p:= 3:

while p < N/2 do

  q:= p;

  p:= nextprime(p);

  r:= (p^2-q^2)/4;

  if r <= N/4 then

    V[r]:= V[r]+1

  fi

od:

map(`*`, select(t -> V[t]=3, [$1..N/4]), 4); # Robert Israel, Aug 13 2018

PROG

(PARI) is(n) = my(i=0, v=[]); forprime(p=5, n, v=[precprime(p-1), p]; if(v[2]^2-v[1]^2==n, i++)); i==3 \\ Felix Fröhlich, Aug 13 2018

CROSSREFS

Cf. A078667, A090784, A090785, A091878.

Sequence in context: A094377 A080395 A092003 * A247724 A236030 A237892

Adjacent sequences:  A090780 A090781 A090782 * A090784 A090785 A090786

KEYWORD

nonn

AUTHOR

Ray G. Opao, Feb 08 2004

EXTENSIONS

More terms from Ray Chandler, Feb 11 2004

STATUS

approved

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Last modified August 9 13:57 EDT 2020. Contains 336323 sequences. (Running on oeis4.)