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A267756
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Indices of Euclid numbers (A006862) of the form x^2 + y^2 + z^2 where x, y and z are integers.
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0
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0, 1, 4, 8, 11, 12, 13, 15, 16, 19, 22, 27, 31, 34, 35, 38, 41, 42, 46, 48, 52, 53, 56, 57, 61, 62, 64, 65, 66, 69, 70, 71, 73, 74, 76, 77, 78, 79, 80, 83, 84, 86, 87, 88, 89, 91, 93, 95, 99, 100, 103, 104, 107, 108, 111, 112, 113, 115, 116, 118, 119, 124, 128, 131, 133
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OFFSET
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1,3
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COMMENTS
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Corresponding Euclid numbers are 2, 3, 211, 9699691, 200560490131, 7420738134811, 304250263527211, 614889782588491411, 32589158477190044731, ...
Complement of this sequence is 2, 3, 5, 6, 7, 9, 10, 14, 17, 18, 20, 21, 23, 24, 25, 26, 28, 29, 30, 32, 33, 36, 37, 39, 40, 43, 44, 45, 47, 49, 50, 51, 54, 55, 58, 59, 60, 63, 67, 68, 72, 75, 81, 82, 85, 90, 92, 94, 96, 97, 98, 101, ...
Euclid numbers that are not of the form x^2 + y^2 + z^2 are 7, 31, 2311, 30031, 510511, 223092871, 6469693231, 13082761331670031, 1922760350154212639071, ...
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LINKS
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EXAMPLE
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0 is a term because A006862(0) = 2 = 0^2 + 1^2 + 1^2.
1 is a term because A006862(1) = 3 = 1^2 + 1^2 + 1^2.
4 is a term because A006862(4) = 211 = 3^2 + 9^2 + 11^2.
8 is a term because A006862(8) = 9699691 = 79^2 + 123^2 + 3111^2.
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PROG
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(PARI) isA004215(n) = { local(fouri, j) ; fouri=1 ; while( n >=7*fouri, if( n % fouri ==0, j= n/fouri -7 ; if( j % 8 ==0, return(1) ) ; ) ; fouri *= 4 ; ) ; return(0) ; }
a006862(n) = prod(k=1, n, prime(k))+1;
for(n=0, 200, if(!isA004215(a006862(n)), print1(n, ", ")));
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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