A272502 Number of n-letter strings over a ten-letter alphabet where no letter appears exactly four times.

1, 10, 100, 1000, 9990, 99550, 987850, 9744850, 95410450, 925825060, 8893045900, 84482314300, 793301261050, 7362408236050, 67558485684790, 613509413395150, 5521782692963800, 49350428808293800, 438963976165310200, 3895008340554766360, 34553010749282271550

Offset

0,2

Comments

Species is SEQ_10(SET_(!=4)(Z)).

Links

Table of n, a(n) for n=0..20.

Math Stackexchange, Marko Riedel et al., N digit numbers with no digit appearing exactly twice.

Formula

E.g.f.: (exp(z)-z^4/4!)^10.

Example

a(4) = 10^4-10 because all 4-letter strings qualify except the strings containing only one type of letter.

Maple

a := n->n!*coeftayl((exp(z)-z^4/4!)^10, z=0, n);

Crossrefs

Cf. A265325, A272501, A272503.

Sequence in context: A136877 A257969 A125904 * A355894 A276596 A190016

Adjacent sequences: A272499 A272500 A272501 * A272503 A272504 A272505

Keyword

base,nonn

Author

Marko Riedel, May 01 2016

Status

approved