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 A213309 Numbers with exactly 2 nonprime substrings (substrings with leading zeros are considered to be nonprime). 1
 11, 12, 15, 19, 20, 21, 24, 26, 28, 30, 34, 36, 38, 39, 41, 42, 45, 50, 51, 54, 56, 58, 61, 62, 63, 65, 70, 74, 76, 78, 82, 85, 87, 89, 92, 93, 95, 113, 131, 179, 197, 227, 229, 231, 232, 235, 239, 253, 257, 271, 273, 277, 283 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The sequence is finite. Proof: Each 6-digit number has at least 4 nonprime substrings. Thus, each number with more than 6 digits has >= 4 nonprime substrings, too. Consequently, there is a boundary b<10^5, such that all numbers > b have more than 2 nonprime substrings. The first term is a(1)=11=A213302(2). The last term is a(130)=37337=A213300(2). LINKS Hieronymus Fischer, Table of n, a(n) for n = 1..130 EXAMPLE a(1)=11, since 11 has 2 nonprime substrings. a(130)= 37337, since there are 2 nonprime substrings (33 and 337). CROSSREFS Cf. A019546, A035232, A039996, A046034, A069489, A085823, A211681, A211682, A211684, A211685. Cf. A035244, A079307, A213300 - A213321. Sequence in context: A045987 A121978 A274566 * A128997 A189836 A292683 Adjacent sequences:  A213306 A213307 A213308 * A213310 A213311 A213312 KEYWORD nonn,fini,base AUTHOR Hieronymus Fischer, Aug 26 2012 STATUS approved

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Last modified November 26 03:20 EST 2020. Contains 338632 sequences. (Running on oeis4.)