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 A116260 n times n+4 gives the concatenation of two numbers m and m-4. 8
 9, 99, 999, 9999, 99999, 999999, 9999999, 99999999, 999999999, 9999999999, 36363636362, 45454545453, 54545454544, 63636363635, 72727272726, 81818181817, 90909090908, 99999999999, 999999999999, 9999999999999 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Chai Wah Wu, Table of n, a(n) for n = 1..121 FORMULA 10^d-1 for d>0 are terms. - Chai Wah Wu, Feb 19 2024 EXAMPLE 99999999 * 100000003 = 100000001//99999997, where // denotes concatenation. PROG (Python) from itertools import count, islice from sympy import sqrt_mod def A116260_gen(): # generator of terms for j in count(0): b = 10**j a = b*10+1 for k in sorted(sqrt_mod(0, a, all_roots=True))+[a]: if a*(b+4) <= k**2 < a*(a+3): yield k-2 A116260_list = list(islice(A116260_gen(), 20)) # Chai Wah Wu, Feb 19 2024 CROSSREFS Cf. A116129, A116254, A116259, A116261, A116267. Sequence in context: A261512 A242809 A108908 * A103456 A002283 A155157 Adjacent sequences: A116257 A116258 A116259 * A116261 A116262 A116263 KEYWORD nonn,base AUTHOR Giovanni Resta, Feb 06 2006 STATUS approved

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Last modified May 17 19:53 EDT 2024. Contains 372607 sequences. (Running on oeis4.)