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 A078667 Integers that occur more than once as the difference of the squares of two consecutive primes. 7
 72, 120, 168, 312, 408, 552, 600, 768, 792, 912, 1032, 1848, 2472, 3048, 3192, 3288, 3528, 3720, 4008, 4920, 5160, 5208, 5808, 5928, 6072, 6480, 6792, 6840, 6888, 7080, 7152, 7248, 7512, 7728, 7800, 8520, 8760, 9072, 11400, 11880, 11928, 12792, 13200, 13320 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 1848 is the first integer that occurs exactly three times. The next few are 6888, 14280, 16008, 19152. 4920 is the first integer that occurs exactly four times. See A069482 for more details. - Richard R. Forberg, Feb 06 2015 LINKS EXAMPLE 120 = 31^2 - 29^2 = 17^2 - 13^2. MATHEMATICA Sort@ DeleteDuplicates@ Flatten@ Select[Gather[NextPrime[#]^2 - #^2 & /@ Prime@ Range@ 1200], Length@ # > 1 &] (* Michael De Vlieger, Mar 18 2015 *) PROG (PARI) pv(v)=vecsort(vecextract(v, concat("1..", vc-1))) op=2; v=vector(5000); vc=1; forprime (p=3, 5000, v[vc]=p^2-op^2; vc++; op=p) v=pv(v) for (i=2, length(v), if (v[i]==v[i-1], print1(v[i]", "))) CROSSREFS Cf. A090783, A090784, A090785, A091878. Sequence in context: A166987 A251124 A169644 * A090784 A291805 A266345 Adjacent sequences:  A078664 A078665 A078666 * A078668 A078669 A078670 KEYWORD nonn AUTHOR Jon Perry, Dec 15 2002 EXTENSIONS Duplicate terms removed, as suggested by Richard R. Forberg, by Jon E. Schoenfield, Mar 15 2015 STATUS approved

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Last modified August 9 22:42 EDT 2020. Contains 336335 sequences. (Running on oeis4.)