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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.)