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 1-4 of 4 results.

A358542 a(n) is the smallest number with exactly n divisors that are tetrahedral numbers.

Original entry on oeis.org

1, 4, 56, 20, 120, 280, 560, 840, 1680, 10920, 9240, 18480, 55440, 120120, 240240, 314160, 628320, 1441440, 2282280, 7225680, 4564560, 9129120, 13693680, 27387360, 54774720, 68468400, 77597520, 136936800, 155195040, 310390080, 465585120, 775975200, 1163962800
Offset: 1

Views

Author

Ilya Gutkovskiy, Nov 21 2022

Keywords

Examples

			a(3) = 56 because 56 has 3 tetrahedral divisors {1, 4, 56} and this is the smallest such number.

Links

Crossrefs

Cf. A000292, A005179, A130317, A279495, A358543, A358544.

Programs

  • PARI
    istetrah(n) = my(k=sqrtnint(6*n, 3)); k*(k+1)*(k+2)==6*n; \\ A000292
a(n) = my(k=1); while (sumdiv(k, d, istetrah(d)) != n, k++); k; \\ Michel Marcus, Nov 21 2022

Extensions

a(20)-a(22) from Michel Marcus, Nov 21 2022
a(23)-a(30) from Jinyuan Wang, Nov 28 2022
a(31) from Martin Ehrenstein, Dec 02 2022
a(32) and a(33) from Lucas A. Brown, Dec 14 2022

A358545 a(n) is the smallest number with exactly n divisors that are centered square numbers.

Original entry on oeis.org

1, 5, 25, 325, 1625, 1105, 5525, 27625, 160225, 1022125, 801125, 5928325, 8491925, 29641625, 42459625, 444215525, 314201225, 2003613625, 1571006125, 14826740825, 12882250225, 127081657625, 64411251125, 88717383625
Offset: 1

Views

Author

Ilya Gutkovskiy, Nov 21 2022

Keywords

Comments

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

Examples

			a(3) = 25 because 25 has 3 centered square divisors {1, 5, 25} and this is the smallest such number.

Links

Crossrefs

Cf. A001844, A005179, A130279, A300410, A358543, A358544.

Programs

  • PARI
    iscsq(n) = issquare(2*n-1); \\ A001844
a(n) = my(k=1); while (sumdiv(k, d, iscsq(d)) != n, k++); k; \\ Michel Marcus, Nov 21 2022

Extensions

a(12)-a(15) from Michel Marcus, Nov 21 2022
a(16) from Martin Ehrenstein, Dec 02 2022
a(17)-a(24) from Jinyuan Wang, Dec 02 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

A359094 a(n) is the smallest square pyramidal number divisible by exactly n square pyramidal numbers.

Original entry on oeis.org

1, 5, 30, 140, 4900, 155155, 6930, 223300, 3573570, 380380, 340889640, 1801800, 333833500, 711410700, 78963134250, 427826509110, 70836325560, 862289508080, 62366724420, 3975527876320, 2279301054030, 3422848288860, 58264695188700, 4903512426212400
Offset: 1

Views

Author

Ilya Gutkovskiy, Dec 16 2022

Keywords

Examples

			a(5) = 4900, because 4900 is a square pyramidal number that has 5 square pyramidal divisors {1, 5, 14, 140, 4900} and this is the smallest such number.

Links

Crossrefs

Cf. A000330, A005179, A130279, A358543, A359095.

Extensions

a(11)-a(24) from Jon E. Schoenfield, Dec 17 2022
Showing 1-4 of 4 results.

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

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