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Concatenation of first 3 digits and last 3 digits of n-th Mersenne prime A000668(n).
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%I #8 Dec 30 2023 16:52:17

%S 33,77,3131,127127,819191,131071,524287,214647,230951,618111,162127,

%T 170727,686151,531127,104087,147007,446351,259071,190991,285607,

%U 478111,346551,281191,431471,448751,402511,854671,536207,521007,512311,746447,174887,129591,412527,814711,623151,127271,437791,924071,125047,299407,122247,315871,124871,202927,169751,316511

%N Concatenation of first 3 digits and last 3 digits of n-th Mersenne prime A000668(n).

%H L. C. Noll, <a href="http://www.isthe.com/chongo/tech/math/prime/mersenne.html">Mersenne Prime Digits and Names</a>.

%t Join[{33,77,3131},FromDigits[Flatten[Join[{Take[IntegerDigits[#],3],Take[ IntegerDigits[ #],-3]}]]]&/@ (2^MersennePrimeExponent[Range[4,40]]-1)] (* _Harvey P. Dale_, Dec 30 2023 *)

%Y Cf. A000668, A080173, A104511, A138816, A138817, A138840, A138841.

%K base,nonn

%O 1,1

%A _Omar E. Pol_, Apr 02 2008

%E More terms from _Harvey P. Dale_, Dec 30 2023