A258276 Balanced sphenic numbers (of order one): sphenic numbers (A007304) that are the average of the previous sphenic number and the following sphenic number.

186, 370, 406, 418, 518, 582, 602, 710, 786, 814, 826, 830, 942, 978, 994, 1010, 1034, 1070, 1162, 1310, 1374, 1394, 1570, 1630, 1686, 1758, 1886, 1978, 2014, 2114, 2158, 2270, 2274, 2278, 2294, 2438, 2510, 2534, 2570, 2630, 2666, 2690, 2774, 2778, 2782, 2806

Offset

1,1

Links

Giovanni Resta, Table of n, a(n) for n = 1..10000

Example

406 is in this sequence because 406 = A007304(45) = (402+410)/2 = (A007304(44) + A007304(46))/2.

Mathematica

a=30; b=42; c=66; L={}; While[ Length[L]<100, If[b-a == c-b, AppendTo[L, b]]; a=b; b=c++; While[ Last/@ FactorInteger[c] != {1, 1, 1}, c++]]; L (* Giovanni Resta, Jun 09 2015 *)

Prog

(PARI)
issphenic(n)=if(n>0, omega(n)==3&&bigomega(n)==3, 0)
nextsph(n)={local(k=n+1); while(!issphenic(k), k+=1); k}
precsph(n)={local(k=n-1); while(!issphenic(k)&&k>0, k-=1); k}
{for(i=1, 4*10^3, if(issphenic(i)&&2*i== nextsph(i)+ precsph(i), print1(i, ", ")))}

Crossrefs

Cf. A006562, A007304, A213025, A245289.

Sequence in context: A363681 A260923 A151701 * A286006 A234108 A200199

Adjacent sequences: A258273 A258274 A258275 * A258277 A258278 A258279

Keyword

nonn

Author

Antonio Roldán, May 25 2015

Status

approved