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A136113
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Pentagonal numbers > 0 which are not the difference of two larger pentagonal numbers.
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6
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1, 5, 12, 35, 51, 92, 117, 176, 330, 477, 782, 852, 1080, 3876, 4347, 7526, 7740, 9801, 13776, 14652, 22632, 24512, 27270, 39285, 69876, 85562, 88452, 103622, 124272, 137562, 144926, 193142, 220992, 268182, 315792, 343922, 354051, 403782, 523626
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OFFSET
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1,2
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LINKS
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Donovan Johnson, Table of n, a(n) for n = 1..500
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FORMULA
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a(n)=A000326(A136112(n)). A number m is in this sequence iff A136114(m) = 0 iff A136115(m) = 0.
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EXAMPLE
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a(1..3)=P(1),P(2),P(3) since these cannot be written as difference of 2 other pentagonal numbers > 0.
P(4)=22=P(8)-P(7), therefore P(4) is not in this sequence.
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PROG
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(PARI) P(n)=n*(3*n-1)>>1 /* a.k.a. A000326 */
isPent(t)=P(sqrtint((t<<1)\3)+1)==t
for( i=1, 999, for( j=i+1, (P(i)-1)\3, isPent(P(i)+P(j))&next(2)); print1(P(i)", "))
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CROSSREFS
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Cf. A000326, A136112-A136118.
Sequence in context: A066280 A192243 A292104 * A298992 A050189 A308344
Adjacent sequences: A136110 A136111 A136112 * A136114 A136115 A136116
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KEYWORD
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nonn
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AUTHOR
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M. F. Hasler, Dec 15 2007, Feb 07 2008
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EXTENSIONS
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a(34)-a(39) from Donovan Johnson, Sep 05 2008
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STATUS
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approved
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