|
| |
|
|
A087600
|
|
Largest n-digit member of A087597, or 0 if no such number exists.
|
|
4
| |
|
|
78, 666, 7503, 82621, 828828, 7552441, 87311505, 557362578, 9901692450, 88893307128, 934624072410, 9836548472766, 99245275962778, 994337011743076, 5535761776004778, 89253915287999385, 865474782199906830, 9888742361454004621
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 2,1
|
|
|
COMMENTS
| Conjecture: No term is zero.
|
|
|
EXAMPLE
| a(4) = 7503, dd(7503) = 253 is triangular.
|
|
|
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) ) ; } 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
|
|
|
CROSSREFS
| Cf. A087597, A087598, A087599.
Sequence in context: A057800 A057806 A057803 * A126994 A129238 A147619
Adjacent sequences: A087597 A087598 A087599 * A087601 A087602 A087603
|
|
|
KEYWORD
| base,nonn
|
|
|
AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Sep 18 2003
|
|
|
EXTENSIONS
| More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Nov 19 2006
a(16)-a(18) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Jul 28 2010
a(19) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Jun 19 2011
|
| |
|
|
