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A269849
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a(n) = number of integers k <= n for which prime(k+1)-prime(k) is not a multiple of three.
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6
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1, 2, 3, 4, 5, 6, 7, 8, 8, 9, 9, 10, 11, 12, 12, 12, 13, 13, 14, 15, 15, 16, 16, 17, 18, 19, 20, 21, 22, 23, 24, 24, 25, 26, 27, 27, 27, 28, 28, 28, 29, 30, 31, 32, 33, 33, 33, 34, 35, 36, 36, 37, 38, 38, 38, 38, 39, 39, 40, 41, 42, 43, 44, 45, 46, 47, 47, 48, 49, 50, 50, 51, 51, 51, 52, 52, 53, 54, 55, 56, 57, 58, 59, 59, 60
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OFFSET
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1,2
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COMMENTS
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a(n) = number of terms of A270189 <= n, the least monotonic left inverse of A270189.
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LINKS
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FORMULA
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Other identities. For all n >= 1:
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MATHEMATICA
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Table[Count[Select[Range@ 125, Mod[Prime[# + 1] - Prime@ #, 3] != 0 &], k_ /; k <= n], {n, 85}] (* Michael De Vlieger, Mar 17 2016 *)
Accumulate[If[Mod[#, 3]==0, 0, 1]&/@Differences[Prime[Range[90]]]] (* Harvey P. Dale, Apr 15 2024 *)
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PROG
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(PARI) a(n) = sum(k=1, n, ((prime(k+1) - prime(k)) % 3) != 0); \\ Michel Marcus, Mar 18 2016
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CROSSREFS
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KEYWORD
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nonn,changed
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AUTHOR
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STATUS
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approved
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