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 A035244 Smallest number with exactly n prime substrings. 49
 1, 2, 13, 23, 113, 137, 373, 1137, 1733, 1373, 11317, 11373, 13733, 31373, 113173, 131373, 137337, 337397, 1113173, 1137337, 1373373, 2337397, 3733797, 11373137, 11373379, 13733797, 37337397, 111373379, 123733739 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS No leading 0's allowed in substrings. The sequence is well-defined in that for each n the set of numbers with n prime substrings is not empty. Proof by induction: '1' has 0 prime substrings and '2' has 1 prime substring. Let m be a number with n prime substrings. Then 10m+2 is a number with n+1 prime substrings (since m and 10m have identical prime substrings, and '2' is one additional prime substring, but 10m+2 cannot be prime). - Hieronymus Fischer, Aug 26 2012 LINKS Hieronymus Fischer, Table of n, a(n) for n = 0..40 FORMULA a(n) > 10^floor((sqrt(8*n-7)-1)/2) for n > 0. - Hieronymus Fischer, Jun 25 2012 Min_{k>=n} a(k) <= A079397(n-1), n > 0. - Hieronymus Fischer, Aug 26 2012 a(n+1) <= 10*a(n) + 2. - Hieronymus Fischer, Aug 26 2012 EXAMPLE a(4)=113 since 3, 11, 13 and 113 are prime and no smaller number works. MATHEMATICA f[n_] := Block[{s = IntegerDigits[n], c = 0, d = {}}, l = Length[s]; t = Flatten[ Table[ Take[s, {i, j}], {i, 1, l}, {j, i, l}], 1]; k = l(l + 1)/2; While[k > 0, If[ t[[k]][] != 0, d = Append[d, FromDigits[ t[[k]] ]]]; k-- ]; Count[ PrimeQ[d], True]]; a = Table[0, {25}]; Do[ b = f[n]; If[ a[[b + 1]] == 0, a[[b + 1]] = n], {n, 1, 15000000}]; a CROSSREFS Cf. A035232, A079397. Sequence in context: A285789 A090528 A094535 * A085822 A213321 A093301 Adjacent sequences:  A035241 A035242 A035243 * A035245 A035246 A035247 KEYWORD base,easy,nonn AUTHOR EXTENSIONS Edited by Robert G. Wilson v, Feb 25 2003 a(25)-a(40) from Hieronymus Fischer, Jun 25 2012 and Aug 25 2012 STATUS approved

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Last modified October 17 17:21 EDT 2021. Contains 348065 sequences. (Running on oeis4.)