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A355279
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Numbers k such that S(S(S(k))) = k, with S(n) = sigma(n)/4: 1/4-sociable numbers of order 1 or 3.
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1
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30240, 32760, 2178540, 23569920, 45532800, 46475520, 48933360, 50995620, 60933600, 69995520, 72807696, 142990848
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OFFSET
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1,1
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COMMENTS
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a(6..11) = { 46475520, 48933360, 50995620, ..., 72807696 } are the first terms not in A027687 (4-perfect numbers), which is obviously a subsequence.
a(11..12) = { 72807696, 142990848 } are the first terms that are not multiples of 60.
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LINKS
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PROG
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(PARI) is_A355279(n, f(x)=if(x && x%4==0, sigma(x\4)))= f(f(sigma(n)))==n*4
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CROSSREFS
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Cf. A113286 (1/4 sociable numbers of order <= 2), A113546 (1/3-sociable numbers).
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KEYWORD
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nonn,more
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AUTHOR
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STATUS
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approved
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