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A337139 Indices m of repunits R_m that are not Colombian (or self) numbers. 4
2, 3, 5, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 73, 74, 75, 76, 77 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Note that 2, 19, 23, 317, 1031, 49081, 86453, 109297, 270343, 5794777, 8177207 (see A004023) are terms. [Last 2 terms added by Serge Batalov, Aug 24 2021]

While all currently known A004023 terms are in this sequence, there is no clear argument that it would hold for all future values. - Serge Batalov, Aug 24 2021

LINKS

David A. Corneth, Table of n, a(n) for n = 1..10000

PROG

(PARI) upto(n)= {my(res = List()); for(i = 1, n, if(is(i), listput(res, i); print1(i", "))); res}

is(n) = {if(n < 8, return(isprime(n))); qd = n; n = 10^n\9; r = 1 + (n-1)%9; h = (r + 9 * (r%2))/2; ld = 10; while(h + 9*qd >= n % ld, ld*=10); vs = qd - valuation(ld, 10); n %= ld; for(i = 0, qd, if(vs + vecsum(digits(n - h - 9*i)) == h + 9*i, return(1))); 0} \\ David A. Corneth, Aug 20 2020

CROSSREFS

Cf. A002275 (repunits), A004022 (repunit primes), A004023 (indices of repunit primes), A176995 (not Colombian).

Cf. A337208 (complement).

Sequence in context: A067792 A119317 A198424 * A039248 A039190 A039142

Adjacent sequences:  A337136 A337137 A337138 * A337140 A337141 A337142

KEYWORD

nonn,base

AUTHOR

Michel Marcus, Aug 19 2020

STATUS

approved

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Last modified November 28 13:47 EST 2021. Contains 349413 sequences. (Running on oeis4.)