

A258276


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


2



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
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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[ba == cb, 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=n1); 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: A189941 A260923 A151701 * A286006 A234108 A200199
Adjacent sequences: A258273 A258274 A258275 * A258277 A258278 A258279


KEYWORD

nonn


AUTHOR

Antonio Roldán, May 25 2015


STATUS

approved



