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A135642
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Concave numbers.
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11
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110, 120, 121, 122, 130, 131, 132, 133, 134, 140, 141, 142, 143, 144, 145, 146, 150, 151, 152, 153, 154, 155, 156, 157, 158, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| The structure of digits represent a concave function or a concave object. In the graphic representation the points are connected by imaginary line segments (or line curves) from left to right.
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EXAMPLE
| The number 12221 is a concave number and the number of this sequence (A135642) is also a concave number:
. . . . . .
. . . . . .
. . . . . .
. . . 6 . .
. . 5 . . .
. . . . 4 .
. 3 . . . .
. . . . . 2
1 . . . . .
. . . . . .
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PROG
| (PARI) { isconcave(n) = local(t); if(n<100, return(0)); t=eval(Vec(Str(n))); for(i=1, #t, for(j=i+2, #t, for(k=i+1, j-1, if( t[k]*(j-i) <= t[i]*(k-i) + t[j]*(j-k), return(0)) ))); 1 } [From Max Alekseyev (maxale(AT)gmail.com), Apr 24 2010]
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CROSSREFS
| Sequence in context: A182621 A036230 A171236 * A166323 A194429 A084042
Adjacent sequences: A135639 A135640 A135641 * A135643 A135644 A135645
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KEYWORD
| nonn,base
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AUTHOR
| Omar E. Pol (info(AT)polprimos.com), Nov 30 2007
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