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A110676
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Number of prime factors with multiplicity of 1 + (n^(n+1)).
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1
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1, 2, 2, 3, 3, 4, 3, 6, 3, 5, 4, 5, 5, 9, 3, 4, 9, 3, 6, 10, 6, 7, 6, 11, 5, 11, 10, 5, 10, 9, 3, 12, 6, 10, 9, 5, 6, 13, 9, 6, 11, 6, 10, 16, 4, 4, 6, 9, 6, 11, 8, 4, 10, 10, 5, 13, 10, 7, 11, 6, 6, 21, 4, 23, 8, 6, 8, 15, 15, 7, 12, 7, 8, 19, 8, 13, 14, 5, 6, 20, 6, 10, 13, 12, 7, 9, 9, 6, 21
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OFFSET
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1,2
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COMMENTS
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As also noticed by T. D. Noe, for odd n: 2 | a(n), for even n: (n+1)^2 | a(n). Coincidentally, a(74) includes 13 multidigit prime factors all of which end with the digit 1. There is no upper limit to this sequence, which rapidly becomes slow to compute. The derived sequences of n such that a(n) = k for any constant k > 2 do not previously appear in OEIS. For instance, a(n) = 3 for n = 4, 5, 7, 9, 15, 18, 31, ... Is each such derived sequence finite?
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LINKS
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Table of n, a(n) for n=1..89.
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FORMULA
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a(1) = 1. For n>1, a(n) = A001222(A110567(n)) = A001222(1 + A007778(n)) = A001222(1 + (n^(n+1))).
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EXAMPLE
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a(1) = 1 because 1+1^2 = 2 is prime (and the only such prime).
a(2) = 2 because 1 + 2^3 = 9 = 3^2 which has (with multiplicity) two prime factors.
a(3) = 2 because 1 + 3^4 = 82 = 2 * 41 (the last such semiprime?).
a(4) = 3 because 1 + 4^5 = 1025 = 5^2 * 41 which has (with multiplicity) 3 prime factors.
a(8) = 6 because 1 + 8^9 = 134217729 = 3^4 * 19 * 87211.
a(14) = 9 because 1 + 14^15 = 155568095557812225 = 3^2 * 5^2 * 61 * 71 * 101 * 811 * 1948981.
a(1000) > 52.
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CROSSREFS
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Cf. A001222, A007778, A110567.
Sequence in context: A127431 A182921 A027833 * A117171 A084054 A106747
Adjacent sequences: A110673 A110674 A110675 * A110677 A110678 A110679
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KEYWORD
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easy,nonn
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AUTHOR
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Jonathan Vos Post, Sep 14 2005
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STATUS
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approved
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