A087599 Smallest nonzero n-digit term of A087597, or 0 if no such number exists.

1, 10, 105, 2211, 16836, 105111, 2220778, 14319276, 221098906, 1087061878, 11402689605, 223577504556, 1264725045100, 50869724563503, 111335989114503, 2399795843858155, 11141229266441550, 127955437456464996, 1070124037258522456

Offset

1,2

Comments

Conjecture: No term is zero.

Links

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

Example

a(4) = 2211, A040115(2211) = 10.

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, Nov 19 2006

Crossrefs

Cf. A000217, A040115, A087597, A087598, A087600.

Sequence in context: A113348 A193274 A068883 * A337826 A226360 A068097

Adjacent sequences: A087596 A087597 A087598 * A087600 A087601 A087602

Keyword

base,nonn

Author

Amarnath Murthy, Sep 18 2003

Extensions

Corrected and extended by R. J. Mathar, Nov 19 2006

a(14)-a(18) from Donovan Johnson, May 08 2010

a(19) from Donovan Johnson, Jun 19 2011

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

Status

approved