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A117388 a(n) is the smallest n-digit integer such that, if all numbers formed by inserting the exponentiation symbol between any two digits are added up, the sum is prime. 2
21, 121, 1226, 14423, 111334, 1186896 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

COMMENTS

No zeros are allowed in the decimal representation of a(n).

LINKS

Table of n, a(n) for n=2..7.

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, Apr 27 2006

CROSSREFS

Cf. A113762.

Sequence in context: A179441 A164785 A179956 * A053052 A243882 A002299

Adjacent sequences:  A117385 A117386 A117387 * A117389 A117390 A117391

KEYWORD

base,more,nonn

AUTHOR

Ray G. Opao, Apr 25 2006

EXTENSIONS

a(6) from Robert G. Wilson v and Farideh Firoozbakht, Apr 27 2006

a(7) from Sean A. Irvine, Dec 15 2009

STATUS

approved

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Last modified January 26 14:08 EST 2020. Contains 331280 sequences. (Running on oeis4.)