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%I #18 Nov 02 2014 12:18:37
%S 3,6,12,18,20,24,48,68,72,80,132,192,258,264,272,384,1032,1040,1088,
%T 1152,1280,2064,2112,4100,4112,4128,4160,5120,6144,8448,16448,20480,
%U 32772,32784,32832,33024,33792,65538,65540,65544,65552,65600,66048,73728,81920,262148,262152,262272,262400,263168,266240,294912,524352,528384,786432
%N Numbers of the form m = 2^i + 2^j, where i > j >= 0, such that m - 1 is prime.
%C Complement of the disjunction of A079696 with A187813. This means that a number m is a term if and only if b = 2 is the only base for which the base-b digital sum of m is b.
%H Hieronymus Fischer, <a href="/A239708/b239708.txt">Table of n, a(n) for n = 1..250</a>
%F A239703(a(n)) = 1.
%e a(1) = 3, since 3 = 2^1 + 2^0.
%e a(3) = 12, since 12 = 2^3 + 2^2.
%o (Smalltalk)
%o A239708
%o "Answers the n-th term of A239708.
%o Usage: n A239708
%o Answer: a(n)"
%o | a b i k m p q terms |
%o terms := OrderedCollection new.
%o b := 2.
%o p := 1.
%o k := 0.
%o m := 0.
%o [k < self] whileTrue:
%o [m := m + 1.
%o p := b * p.
%o q := 1.
%o i := 0.
%o [i < m and: [k < self]] whileTrue:
%o [i := i + 1.
%o a := p + q.
%o (a - 1) isPrime
%o ifTrue:
%o [k := k + 1.
%o terms add: a].
%o q := b * q]].
%o ^terms at: self
%o -----------------
%o (Smalltalk)
%o A239708inv
%o "Answers a kind of inverse of A239708.
%o Usage: n A239708inv
%o Answer: max ( k | A239708(k) < n)"
%o | k |
%o k := 1.
%o [k A239708 < self] whileTrue: [k := k + 1].
%o ^k - 1
%Y Cf. A239709 - A239720.
%Y Cf. A239703, A187813, A079696, A008864.
%K nonn
%O 1,1
%A _Hieronymus Fischer_, Mar 27 2014
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