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 A090841 Smallest prime whose product of digits is 7^n. 5
 11, 7, 11177, 1777, 71777, 1777717, 1177717771, 77777177, 7177717777, 1777777777, 71777777777, 1717777777777, 7177777777777, 17777777777777, 17177777777777717, 7717777777777777, 1177777777177777777 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS EXAMPLE a(6) = 1177717771 because its digital product is 7^6. MATHEMATICA NextPrim[n_] := Block[{k = n + 1}, While[ !PrimeQ[k], k++ ]; k]; a = Table[0, {18}]; p = 2; Do[q = Log[7, Times @@ IntegerDigits[p]]; If[q != 0 && IntegerQ[q] && a[[q]] == 0, a[[q]] = p; Print[q, " = ", p]]; p = NextPrim[p], {n, 1, 10^9}] For a(8); a = Map[ FromDigits, Permutations[{1, 1, 7, 7, 7, 7, 7, 7, 7, 7}]]; Min[ Select[a, PrimeQ[ # ] &]] CROSSREFS Cf. A089365, A088653, A090840, A091465, A089298. Sequence in context: A002749 A055505 A159526 * A085757 A003567 A085688 Adjacent sequences:  A090838 A090839 A090840 * A090842 A090843 A090844 KEYWORD base,nonn AUTHOR Robert G. Wilson v, Dec 09 2003 STATUS approved

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Last modified June 17 17:43 EDT 2021. Contains 345085 sequences. (Running on oeis4.)