A072956 Turban numbers: without letters r, t, or u.

1, 5, 6, 7, 9, 11, 1000000, 1000001, 1000005, 1000006, 1000007, 1000009, 1000011, 5000000, 5000001, 5000005, 5000006, 5000007, 5000009, 5000011, 6000000, 6000001, 6000005, 6000006, 6000007, 6000009, 6000011, 7000000, 7000001, 7000005, 7000006, 7000007, 7000009

Offset

1,2

References

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

Links

Michael S. Branicky, Table of n, a(n) for n = 1..10000

Prog

(PARI) is(n)=!setintersect(Set(Vec(English(n))), ["r", "t", "u"]) \\ See A052360 for English(). - M. F. Hasler, Apr 01 2019
(Python)
from num2words import num2words
from itertools import islice, product
def ok(n): return set(num2words(n)) & {"r", "t", "u"} == set()
def agen(): # generator of terms < 10**304
    base, pows = [k for k in range(1, 1000) if ok(k)], [1]
    yield from ([0] if ok(0) else []) + base
    for e in range(3, 304, 3):
        if set(num2words(10**e)[4:]) & {"r", "t", "u"} == set():
            pows = [10**e] + pows
            for t in product([0] + base, repeat=len(pows)):
                if t[0] == 0: continue
                yield sum(t[i]*pows[i] for i in range(len(t)))
print(list(islice(agen(), 66))) # Michael S. Branicky, Aug 19 2022

Crossrefs

Cf. A006933 (eban numbers: without 'e'), A008521 (without 'o'), A008523 (without 't'), A008537 (without 'n'), A089590 (without 'u'), A072957 (urban numbers: without r or u), A089589 (without 'i').

Sequence in context: A180939 A229231 A073419 * A241203 A279001 A080708

Adjacent sequences: A072953 A072954 A072955 * A072957 A072958 A072959

Keyword

easy,nonn,word

Author

Michael Joseph Halm, Aug 13 2002

Status

approved