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A213309
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Numbers with exactly 2 nonprime substrings (substrings with leading zeros are considered to be nonprime).
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1
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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
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OFFSET
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1,1
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COMMENTS
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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).
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LINKS
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EXAMPLE
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a(1)=11, since 11 has 2 nonprime substrings.
a(130)= 37337, since there are 2 nonprime substrings (33 and 337).
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CROSSREFS
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KEYWORD
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nonn,fini,base
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AUTHOR
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STATUS
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approved
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