A138844 -id:A138844 - cp's OEIS frontend

A138843 Concatenation of initial and final digits of n-th perfect number.

66, 28, 46, 88, 36, 86, 18, 28, 26, 16, 18, 18, 26, 18, 58, 18, 96, 36, 16, 48, 16, 56, 36, 96, 16, 86, 36, 18, 18, 16, 28, 18, 86, 88, 36, 16, 86, 96, 46

Offset: 1

Omar E. Pol, Apr 02 2008

Also, concatenation of A135617(n) and A094540(n).

			a(5)=36 because the 5th perfect number A000396(5) is 33550336 and the concatenation of initial and final digits of 33550336 is 36.

Cf. A000396, A073729, A135617, A094540, A138840, A138841, A138842, A138844.

A138840 Concatenation of initial and final digits of n-th prime.

Original entry on oeis.org

22, 33, 55, 77, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 11, 13, 17, 19, 13, 17, 11, 17, 19, 19, 11, 17, 13, 17, 13, 19, 11, 11, 13, 17, 19, 21, 23, 27, 29, 23, 29, 21, 21, 27, 23, 29, 21, 27, 21, 23, 23, 37, 31, 33, 37, 31, 37, 37

Offset: 1

Omar E. Pol, Apr 01 2008

There are only 38 distinct terms in this sequence, all of them odd with the exception of 22. 55 is the only term divisible by 5. 22 and 55 each appear only once. The other terms, each of which appears multiple times, are the odd two-digit numbers not divisible by 5. - Harvey P. Dale, May 15 2012

a(n) is the concatenation of A077648(n) and A007652(n), hence all terms of this sequence have two digits in the same way as A073729. - Omar E. Pol, Mar 23 2018

Harvey P. Dale, Table of n, a(n) for n = 1..1000
Omar E. Pol, Determinacion geometrica de los numeros primos y perfectos.

Cf. A000040, A007652, A073729, A077648, A138841, A138842, A138843, A138844.

Cf. A137589 (same except for first four terms).

a:= n-> (p-> parse(cat(p[1], p[-1])))(""||(ithprime(n))):
seq(a(n), n=1..92);  # Alois P. Heinz, Nov 23 2023

cifd[n_]:=Module[{il=IntegerLength[n],idn=IntegerDigits[n]},Which[ il==1, 10n+n, il==2,n,il>2,FromDigits[Join[{First[idn],Last[idn]}]]]]; cifd/@ Prime[ Range[70]] (* Harvey P. Dale, May 15 2012 *)

a(n) = my(d=digits(prime(n))); fromdigits(concat(d[1], d[#d])); \\ Michel Marcus, Mar 23 2018

A138842 Concatenation of initial and final digits of n-th even superperfect number A061652(n).

Original entry on oeis.org

22, 44, 16, 64, 46, 66, 24, 14, 16, 36, 84, 84, 36, 24, 54, 74, 26, 16, 96, 14, 26, 16, 16, 26, 26, 26, 46, 24, 24, 26, 34, 84, 66, 24, 46, 36, 66, 26, 46, 64, 14, 64, 16, 66, 14, 86, 16

Offset: 1

Omar E. Pol, Apr 02 2008

Also, concatenation of initial and final digits of n-th superperfect number A019279(n), if there are no odd superperfect numbers.

Also, concatenation of A138124(n) and A138125(n).

Cf. A019279, A061652, A073729, A138124, A138125, A138838, A138840, A138841, A138843, A138844.

More terms from Jinyuan Wang, Mar 14 2020

A367556 Comma transform of the Fibonacci numbers.

Original entry on oeis.org

1, 11, 12, 23, 35, 58, 81, 32, 13, 45, 58, 91, 42, 33, 76, 9, 71, 72, 44, 16, 51, 61, 12, 74, 87, 51, 31, 83, 15, 98, 1, 92, 93, 85, 79, 51, 22, 73, 96, 61, 51, 12, 64, 77, 31, 1, 32, 34, 67, 91, 52, 43, 95, 38, 21, 52, 73, 25, 99, 11, 2, 14, 16, 21, 31, 52, 84

Offset: 0

Alois P. Heinz, Nov 22 2023

See A367360 for further information.

Alois P. Heinz, Table of n, a(n) for n = 0..10000

Cf. A000045, A003893, A008963, A138844, A367360.

F:= combinat[fibonacci]:
a:= n-> parse(cat(""||(F(n))[-1], ""||(F(n+1))[1])):
seq(a(n), n=0..92);

With[{nmax=100},Map[10Mod[#[[1]],10]+IntegerDigits[#[[2]]][[1]]&,Partition[Fibonacci[Range[0,nmax+1]],2,1]]] (* Paolo Xausa, Nov 24 2023 *)

from sympy import fibonacci
from itertools import islice, pairwise, count
def S(): yield from (fibonacci(i) for i in count(0))
def C(g): # generator of comma transform of sequence passed as a generator
    yield from (10*(t%10) + int(str(u)[0]) for t, u in pairwise(g))
def agen(): return C(S())
print(list(islice(agen(), 67))) # Michael S. Branicky, Jan 05 2024

a(n) = 10 * A003893(n) + A008963(n+1).

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A138843 Concatenation of initial and final digits of n-th perfect number.

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A138840 Concatenation of initial and final digits of n-th prime.

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A138842 Concatenation of initial and final digits of n-th even superperfect number A061652(n).

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A367556 Comma transform of the Fibonacci numbers.

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