**a(n) = Sum[5^i, {i, 0, n}] + 1 - Mod[Sum[5^i, {i, 0, n}], 2]**

*1, 7, 31, 157, 781, 3907, 19531, 97657, 488281, 2441407, 12207031, 61035157*

*1 seqfan posts*

Index of A-numbers in seqfan: by ascending order by month by frequency by keyword

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