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 A275340 Nontrivial centered polygonal numbers: numbers of the form A101321(n,k) where n>=1 and k>=2. 4
 4, 7, 10, 11, 13, 16, 19, 21, 22, 25, 28, 29, 31, 34, 37, 40, 41, 43, 46, 49, 51, 52, 55, 56, 57, 58, 61, 64, 67, 70, 71, 73, 76, 79, 81, 82, 85, 88, 91, 92, 94, 97, 100, 101, 103, 106, 109, 111, 112, 113, 115, 118, 121, 124, 127, 130, 131, 133, 136, 137, 139, 141, 142, 145, 148, 151 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS This is a centered polygonal number analog to A090466. LINKS Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 FORMULA a(n) ~ cn with 1.95 < c < 2.29. - Charles R Greathouse IV, Jul 28 2016 MAPLE isA275340 := proc(n)     local nsearch, ksearch;     for nsearch from 1 do         if A101321(nsearch, 2) > n then             return false;         end if;         for ksearch from 2 do             if A101321(nsearch, ksearch) = n then                 return true;             elif A101321(nsearch, ksearch) > n then                 break;             end if;         end do:     end do: end proc: for n from 1 to 400 do     if isA275340(n) then         printf("%d, ", n) ;     end if; end do: PROG (PARI) list(lim)=my(v=List(), t); lim\=1; for(k=2, sqrt(8*lim-7)/2, t=k*(k+1)/2; forstep(a=t+1, lim, t, listput(v, a))); Set(v) \\ Charles R Greathouse IV, Jul 28 2016 CROSSREFS Cf. A101321. Sequence in context: A123869 A072125 A223024 * A082206 A115566 A190507 Adjacent sequences:  A275337 A275338 A275339 * A275341 A275342 A275343 KEYWORD nonn AUTHOR R. J. Mathar, Jul 28 2016 STATUS approved

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Last modified November 12 22:01 EST 2018. Contains 317116 sequences. (Running on oeis4.)