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 A090781 Numbers that can be expressed as the difference of the squares of primes in just one distinct way. 27
 5, 16, 21, 24, 40, 45, 48, 96, 112, 117, 144, 160, 165, 192, 264, 280, 285, 288, 336, 352, 357, 504, 520, 525, 648, 816, 832, 837, 936, 952, 957, 1152, 1344, 1360, 1365, 1368, 1440, 1656, 1672, 1677, 1752, 1824, 1840, 1845, 1872, 1968, 2184, 2200, 2205, 2328 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS T. D. Noe, Table of n, a(n) for n=1..908 EXAMPLE 5 = 3^2 - 2^2. MATHEMATICA With[{nn=100}, Take[Sort[Transpose[Select[Tally[Last[#]-First[#]&/@ Subsets[ Prime[Range[nn]]^2, {2}]], Last[#]==1&]][[1]]], nn]] (* Harvey P. Dale, Apr 05 2014 *) PROG (Python) from sympy import primerange from collections import Counter def aupto(limit): sqps = [p*p for p in primerange(1, limit//2+1)] ways = Counter(b-a for i, a in enumerate(sqps) for b in sqps[i+1:]) return sorted(k for k in ways if k <= limit and ways[k] == 1) print(aupto(2328)) # Michael S. Branicky, May 16 2021 CROSSREFS Cf. A078667, A090788, A090782, A090785. Sequence in context: A204920 A168469 A124865 * A191264 A077469 A022140 Adjacent sequences: A090778 A090779 A090780 * A090782 A090783 A090784 KEYWORD nonn AUTHOR Ray Chandler, Feb 14 2004 STATUS approved

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Last modified September 21 16:01 EDT 2023. Contains 365502 sequences. (Running on oeis4.)