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Search: id:A087600
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| A087600 |
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Largest n-digit member of A087597, or 0 if no such number exists. |
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+0
4
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| 78, 666, 7503, 82621, 828828, 7552441, 87311505, 557362578, 9901692450, 88893307128, 934624072410, 9836548472766, 99245275962778, 994337011743076
(list; graph; listen)
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OFFSET
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2,1
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COMMENT
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Conjecture: No term is zero.
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EXAMPLE
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a(4) = 7503, dd(7503) = 253 is triangular.
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PROGRAM
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(PARI) dd(k)={ local(kshf, res, dig, odig, p) ; kshf=k ; res=0 ; odig=kshf % 10 ; p=0 ; while(kshf>9, kshf=floor(kshf/10) ; dig=kshf % 10 ; res += 10^p*abs(dig-odig) ; odig=dig ; p++ ; ) ; return(res) ; } isA000217(n)={ if( issquare(1+8*n), return(1), return(0) ) ; } A000217(n)={ return(n*(n+1)/2) ; } ndigs(n)={ local(nshft, res) ; res=0 ; nshft=n; while(nshft>0, res++ ; nshft=floor(nshft/10) ; ) ; return(res) ; } isA087597(n)={ if( isA000217(n) && isA000217(dd(n)), return(1), return(0) ) ; } A087600(n)={ local(k, T) ; k=ceil(-0.5+sqrt(0.25+2*10^n)) ; T=A000217(k) ; if(ndigs(T)>n, k-- ) ; while(1, T=A000217(k) ; if(ndigs(T)<n, return(0) ) ; if( isA087597(T), return(T) ) ; k-- ; ) ; } { for(n=2, 21, print1(A087600(n), ", ") ; ) ; } - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Nov 19 2006
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CROSSREFS
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Cf. A087597, A087598, A087599.
Sequence in context: A057800 A057806 A057803 this_sequence A126994 A129238 A147619
Adjacent sequences: A087597 A087598 A087599 this_sequence A087601 A087602 A087603
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KEYWORD
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base,more,nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Sep 18 2003
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EXTENSIONS
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More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Nov 19 2006
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