来自在线整数百科全书的问候语!http://oeis.org/ Search: id:a087600 Showing 1-1 of 1 %I A087600 %S A087600 78,666,7503,82621,828828,7552441,87311505,557362578,9901692450, %T A087600 88893307128,934624072410,9836548472766,99245275962778, %U A087600 994337011743076,5535761776004778,89253915287999385,865474782199906830,9888742361454004621 %N A087600 Largest n-digit member of A087597, or 0 if no such number exists. %C A087600 Conjecture: No term is zero. %e A087600 a(4) = 7503, dd(7503) = 253 is triangular. %o A087600 (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=A000 0217(k);IF(nDigs(t)>n,k-);(1)t= a000 0217(k);If(nDigs(t))-->