A087600 Largest n-digit term of A087597, or 0 if no such number exists.

6, 78, 666, 7503, 82621, 828828, 7552441, 87311505, 557362578, 9901692450, 88893307128, 934624072410, 9836548472766, 99245275962778, 994337011743076, 5535761776004778, 89253915287999385, 865474782199906830, 9888742361454004621

Offset

1,1

Comments

Conjecture: No term is zero.

Links

Table of n, a(n) for n=1..19.

Example

a(4) = 7503, A040115(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, Nov 19 2006

Crossrefs

Cf. A000217, A087597, A087598, A087599.

Sequence in context: A160240 A069669 A145359 * A306096 A370714 A145360

Adjacent sequences: A087597 A087598 A087599 * A087601 A087602 A087603

Keyword

base,nonn

Author

Amarnath Murthy, Sep 18 2003

Extensions

More terms from R. J. Mathar, Nov 19 2006

a(16)-a(18) from Donovan Johnson, Jul 28 2010

a(19) from Donovan Johnson, Jun 19 2011

a(1)=6 prepended by Max Alekseyev, Jul 27 2024

Status

approved