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A072668
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Numbers one less than composite numbers.
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15
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3, 5, 7, 8, 9, 11, 13, 14, 15, 17, 19, 20, 21, 23, 24, 25, 26, 27, 29, 31, 32, 33, 34, 35, 37, 38, 39, 41, 43, 44, 45, 47, 48, 49, 50, 51, 53, 54, 55, 56, 57, 59, 61, 62, 63, 64, 65, 67, 68, 69, 71, 73, 74, 75, 76, 77, 79, 80, 81, 83, 84, 85, 86, 87, 89, 90, 91, 92, 93, 94, 95
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OFFSET
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1,1
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COMMENTS
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Complement of A006093 (primes minus 1).
Numbers which can be written as i*j+i+j, 0<i<=j: A072670(a(n))>0 for n>1.
a(n)! is divisible by a(n)*(a(n)+1)/2, see A060462.
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LINKS
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FORMULA
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MATHEMATICA
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PROG
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(PARI) for(n=2, 100, if(!isprime(n), print1(n-1, ", "))) \\ Derek Orr, Jun 08 2015
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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