cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-3 of 3 results.

A358861 a(n) is the smallest centered n-gonal number divisible by exactly n centered n-gonal numbers.

Original entry on oeis.org

64, 925, 2976, 93457, 866272, 11025, 3036880, 18412718645101, 9283470627432, 201580440699781, 92839099743040, 5236660451226975, 66779973961058176
Offset: 3

Views

Author

Ilya Gutkovskiy, Dec 03 2022

Keywords

Comments

a(17) = 1415913990579036. - Daniel Suteu, Dec 10 2022

Examples

			a(5) = 2976, because 2976 is a centered pentagonal number that has 5 centered pentagonal divisors {1, 6, 16, 31, 2976} and this is the smallest such number.

Links

Crossrefs

Cf. A005179, A358541, A358859, A358860.

Programs

  • PARI
    a(n) = if(n<3, return()); for(k=1, oo, my(t=((n*k*(k+1))/2+1)); if(sumdiv(t, d, issquare(8*(d-1)/n + 1) && (sqrtint((8*(d-1))/n + 1)-1)%2 == 0) == n, return(t))); \\ Daniel Suteu, Dec 10 2022

Extensions

a(10)-a(15) from Daniel Suteu, Dec 06 2022

A358539 a(n) is the smallest number with exactly n divisors that are n-gonal numbers.

Original entry on oeis.org

6, 36, 210, 1260, 6426, 3360, 351000, 207900, 3749460, 1153152, 15036840, 204204000, 213825150, 11737440, 91797866160, 1006485480, 2310808500, 4966241280, 22651328700, 325269404460, 14266470332400, 11203920000, 256653797400, 45843256859400, 59207908359600, 46822406400
Offset: 3

Views

Author

Ilya Gutkovskiy, Nov 21 2022

Keywords

Examples

			a(5) = 210 because 210 has 5 pentagonal divisors {1, 5, 35, 70, 210} and this is the smallest such number.

Links

Crossrefs

Cf. A005179, A130279, A130317, A356132, A358540, A358541.

Programs

  • PARI
    a(n) = my(k=1); while (sumdiv(k, d, ispolygonal(d, n)) != n, k++); k; \\ Michel Marcus, Nov 21 2022

Extensions

a(12)-a(13) from Michel Marcus, Nov 21 2022
a(14)-a(16) from Daniel Suteu, Dec 04 2022
a(17)-a(28) from Martin Ehrenstein, Dec 05 2022

A358540 a(n) is the smallest number with exactly n divisors that are n-gonal pyramidal numbers.

Original entry on oeis.org

56, 140, 1440, 11550, 351120, 41580, 742560, 29279250, 8316000, 72348396120, 3386892600, 578918340
Offset: 3

Views

Author

Ilya Gutkovskiy, Nov 21 2022

Keywords

Comments

Any subsequent terms are > 2 * 10^9. - Lucas A. Brown, Dec 24 2022

Examples

			a(5) = 1440 because 1440 has 5 pentagonal pyramidal divisors {1, 6, 18, 40, 288} and this is the smallest such number.

Links

Crossrefs

Cf. A005179, A358539, A358541, A358542, A358543.

Extensions

a(11)-a(13) from Martin Ehrenstein, Dec 02 2022
a(14) from Lucas A. Brown, Dec 19 2022
Showing 1-3 of 3 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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