A117388 - OEIS

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A117388

a(n) is the smallest n-digit integer such if all numbers formed by inserting the exponentation symbol between any two digits are added up, the sum is prime.

21, 121, 1226, 14423, 111334, 1186896 (list; graph; refs; listen; history; internal format)

	OFFSET	`2,1`
	COMMENTS	`No zeros are allowed in the decimal representation of a(n).`
	EXAMPLE	`a(5) = 14423 since 1^4423+14^423+144^23+1442^3 is prime.`
	MATHEMATICA	(* first do ) Needs["DiscreteMath`Combinatorica`"] ( then *) f[n_] := Block[{k = (10^n - 1)/9}, While[id = IntegerDigits@k; First@ Union@ id == 0 \|\| !PrimeQ[Plus @@ Table[FromDigits@ Take[id, {1, k}]^FromDigits@ Take[id, {k + 1, n}], {k, n - 1}]], k++ ]; k]; Do[Print[f[n]] // Timing, {n, 2, 7}] - Robert G. Wilson v (rgwv(at)rgwv.com), Apr 27 2006
	CROSSREFS	`Cf. A113762.` `Sequence in context: A179441 A164785 A179956 * A053052 A002299 A041852` `Adjacent sequences: A117385 A117386 A117387 * A117389 A117390 A117391`
	KEYWORD	`base,more,nonn`
	AUTHOR	`Ray G. Opao (1260(AT)email.com), Apr 25 2006`
	EXTENSIONS	`a(6) from Robert G. Wilson v (rgwv(at)rgwv.com) and Farideh Firoozbakht (mymontain(AT)yahoo.com), Apr 27 2006` `a(7) from Sean A. Irvine (sairvin(AT)xtra.co.nz), Dec 15 2009`

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Last modified February 15 23:53 EST 2012. Contains 205860 sequences.