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A087599
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Smallest n-digit member of A087597, or 0 if no such number exists.
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4
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10, 105, 2211, 16836, 105111, 2220778, 14319276, 221098906, 1087061878, 11402689605, 223577504556, 1264725045100, 50869724563503, 111335989114503, 2399795843858155, 11141229266441550, 127955437456464996, 1070124037258522456
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,1
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COMMENTS
| Conjecture: No term is zero.
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EXAMPLE
| a(4)=2211, dd(2211)=010=10.
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PROG
| (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) ) ; } A087599(n)={ local(k, T) ; k=floor(-0.5+sqrt(0.25+2*10^(n-1))) ; 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(A087599(n), ", ") ; ) ; } - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Nov 19 2006
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CROSSREFS
| Cf. A087597, A087598, A087600.
Sequence in context: A113348 A193274 A068883 * A068097 A190956 A142987
Adjacent sequences: A087596 A087597 A087598 * A087600 A087601 A087602
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KEYWORD
| base,nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Sep 18 2003
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EXTENSIONS
| Corrected and extended by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Nov 19 2006
a(14)-a(18) from Donovan Johnson (donovan.johnson(AT)yahoo.com), May 08 2010
a(19) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Jun 19 2011
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