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 A103381 Numbers which are the sum of four distinct squares, a^2+b^2+c^2+d^2, such that a^2+b^2, c^2+d^2, a^2+d^2 and b^2+c^2 are all prime. 3
 46, 66, 78, 102, 114, 126, 142, 154, 162, 174, 198, 222, 246, 262, 270, 274, 282, 286, 294, 298, 318, 322, 334, 342, 354, 366, 378, 382, 394, 402, 406, 414, 426, 438, 442, 454, 462, 486, 498, 502, 510, 518, 522, 526, 534, 538, 546, 550, 558, 562, 574, 582 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Such primes must be == 1 mod 4. All the terms of the sequence are of the form 4*k+2. LINKS Table of n, a(n) for n=1..52. EXAMPLE 46 = 1^2+2^2+5^2+4^2 = 5+41 = 17+29 102 = 3^2+2^2+5^2+8^2 = 13+89 = 73+29 MATHEMATICA t = Partition[ Flatten[ Table[{a^2 + b^2 + c^2 + d^2, a^2, b^2, c^2, d^2}, {d, 4, 20}, {c, 3, d - 1}, {b, 2, c - 1}, {a, b - 1}]], 5]; lst = {}; lg = Length[t]; Do[a = t[[n, 2]]; b = t[[n, 3]]; c = t[[n, 4]]; d = t[[n, 5]]; If[ Drop[ Sort[ Join[ {Mod[a + b, 4] == 1 && Mod[c + d, 4] == 1 && PrimeQ[a + b] && PrimeQ[c + d]}, {Mod[a + c, 4] == 1 && Mod[b + d, 4] == 1 && PrimeQ[a + c] && PrimeQ[b + d]}, {Mod[a + d, 4] == 1 && Mod[b + c, 4] == 1 && PrimeQ[a + d] && PrimeQ[b + c]}]], 1] == {True, True}, AppendTo[ lst, t[[n, 1]] ]], {n, lg}]; Take[ Union[ lst], 52] (* Robert G. Wilson v, Mar 25 2005 *) apQ[{a_, b_, c_, d_}]:=AllTrue[{a+b, c+d, a+d, b+c}, PrimeQ]; Total/@Select[ Flatten[ Permutations/@Subsets[Range[20]^2, {4}], 1], apQ]//Union (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Jul 22 2018 *) CROSSREFS Sequence in context: A020175 A118698 A350203 * A101577 A051413 A167283 Adjacent sequences: A103378 A103379 A103380 * A103382 A103383 A103384 KEYWORD nonn AUTHOR Robin Garcia, Mar 20 2005 EXTENSIONS Edited by Don Reble and Robert G. Wilson v, Mar 25 2005 STATUS approved

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Last modified May 22 06:48 EDT 2024. Contains 372743 sequences. (Running on oeis4.)