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Initial digit of n-th even superperfect number A061652(n).
4

%I #11 Mar 14 2015 19:30:18

%S 2,4,1,6,4,6,2,1,1,3,8,8,3,2,5,7,2,1,9,1,2,1,1,2,2,2,4,2,2,2,3,8,6,2,

%T 4,3,6,2,4

%N Initial digit of n-th even superperfect number A061652(n).

%C Also, initial digit of n-th superperfect number A019279(n), if there are no odd superperfect numbers.

%e a(5)=4 because the 5th even superperfect number A061652(5) is 4096 and the initial digit of 4096 is 4.

%t lst = {2, 3, 5, 7, 13, 17, 19, 31, 61, 89, 107, 127, 521, 607, 1279, 2203, 2281, 3217, 4253, 4423, 9689, 9941, 11213, 19937, 21701, 23209, 44497, 86243, 110503, 132049, 216091, 756839, 859433, 1257787, 1398269, 2976221, 3021377, 6972593, 13466917}; f[n_] := Block[{pn = 2^(n - 1)}, Quotient[pn, 10^Floor[Log[10, pn]]]]; f@# & /@ (* _Robert G. Wilson v_, Apr 01 2008 *)

%Y Cf. A000030, A077648, A019279, A061652, A135613, A135617, A138125.

%K base,nonn

%O 1,1

%A _Omar E. Pol_ and _Robert G. Wilson v_, Apr 01 2008

%E a(13)-a(39) from _Robert G. Wilson v_, Apr 01 2008