A073418 Useless numbers: numbers written in English without any of the letters e, s or u.

2, 30, 32, 40, 42, 50, 52, 2000000, 2000002, 2000030, 2000032, 2000040, 2000042, 2000050, 2000052, 30000000, 30000002, 30000030, 30000032, 30000040, 30000042, 30000050, 30000052, 32000000, 32000002, 32000030, 32000032, 32000040, 32000042, 32000050, 32000052

Offset

1,1

Comments

After a(7), the sequence contains only terms of the form a(i) * 10^(3*k) and a(i) * 10^(3*k) + a(j) for 1 <= i, j <= 7, where the name of 10^(3*k) is useless, e.g., 10^6 (million), 10^9 (billion), 10^12 (trillion), 10^27 (octillion), 10^30 (nonillion), ... (see links for large number names). - Michael S. Branicky, Jan 01 2021

Links

Table of n, a(n) for n=1..31.

M. J. Halm, Sequences (Re)discovered, Mpossibilities 81 (Aug. 2002).

Eric Weisstein's World of Mathematics, Large Number

Wikipedia, Names of Large Numbers

Example

a(2) = 30 because 30 is the second integer without an e, s or u in its English name.

Crossrefs

Sequence in context: A228937 A071056 A075716 * A022377 A145290 A343930

Adjacent sequences: A073415 A073416 A073417 * A073419 A073420 A073421

Keyword

nonn,word

Author

Michael Joseph Halm, Aug 23 2002

Extensions

Removed 'ninety' and 'ninety two' from the sequence which clearly include the letter E. Likewise removed 'two hundrEd' and others. Inserted 'thirty' and 'thirty-two'. - Freddie Noble, Jan 01 2021

a(16)-a(31) from Michael S. Branicky, Jan 01 2021

Status

approved