A049104 -id:A049104 - cp's OEIS frontend

A049103 Numbers k such that k and k+1 both have 6 divisors.

44, 75, 98, 116, 147, 171, 242, 243, 244, 332, 387, 507, 548, 603, 604, 724, 844, 908, 931, 963, 1075, 1083, 1251, 1324, 1412, 1467, 1556, 1587, 1675, 1772, 2523, 2524, 2636, 2644, 2763, 3283, 3356, 3411, 3508, 3788, 3987, 4075, 4203, 4204, 4418, 4491, 4804, 4868, 4923, 4924

Offset: 1

N. J. A. Sloane, Felice Russo, Olivier Gérard

nonn

David Wells, The Penguin Dictionary of Curious and Interesting Numbers, Penguin Books, 1986, entry 44, p. 103.

Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Vincenzo Librandi)

Intersection of A005237 and A030515.

Cf. A038400, A049104.

Flatten[Position[Partition[Table[DivisorSigma[0,n],{n,5000}],2,1],?(# == {6,6}&)]] (* _Harvey P. Dale, Apr 09 2012 *)

isok(n) = (numdiv(n) == 6) && (numdiv(n+1) == 6); \\ Michel Marcus, Feb 11 2016

a(n) = A049104(n) - 1. - Zak Seidov, Feb 11 2016

A066308 a(n) = (sum of digits of n) * (product of digits of n).

Original entry on oeis.org

1, 4, 9, 16, 25, 36, 49, 64, 81, 0, 2, 6, 12, 20, 30, 42, 56, 72, 90, 0, 6, 16, 30, 48, 70, 96, 126, 160, 198, 0, 12, 30, 54, 84, 120, 162, 210, 264, 324, 0, 20, 48, 84, 128, 180, 240, 308, 384, 468, 0, 30, 70, 120, 180, 250, 330, 420, 520, 630, 0, 42, 96, 162, 240, 330

Offset: 1

Labos Elemer, Dec 13 2001

a(n) can be greater than, less than, or equal to n; see Example section.

			For n = 12, a(12) = (1 + 2)*(1*2) = 3*2 = 6 < n;
for n = 19, a(19) = (1 + 9)*(1*9) = 90 > n;
for n = 135, a(135) =(1 + 3 + 5)*(1*3*5) = 135 = n.

Harry J. Smith, Table of n, a(n) for n = 1..1000

Cf. A007953, A007954.
Cf. A038369 (fixed points), A034710, A061672.
Cf. A049101, A049102, A049103, A049104, A049105, A049106.

asum[x_] := Apply[Plus, IntegerDigits[x]] apro[x_] := Apply[Times, IntegerDigits[x]] a[n]=asum[n]*apro[n]
sdpd[n_]:=Module[{idn=IntegerDigits[n]},Total[idn]Times@@idn]; Array[ sdpd,70] (* Harvey P. Dale, Dec 31 2011 *)

a(n) = my(d = digits(n)); vecsum(d) * vecprod(d); \\ Michel Marcus, Feb 24 2017

Edited by Jon E. Schoenfield, Jul 09 2018

A038400 List of pairs of consecutive numbers each with 6 divisors (duplicates removed).

Original entry on oeis.org

44, 45, 75, 76, 98, 99, 116, 117, 147, 148, 171, 172, 242, 243, 244, 245, 332, 333, 387, 388, 507, 508, 548, 549, 603, 604, 605, 724, 725, 844, 845, 908, 909, 931, 932, 963, 964, 1075, 1076, 1083, 1084, 1251, 1252, 1324, 1325, 1412, 1413, 1467, 1468, 1556, 1557, 1587, 1588

Offset: 1

Felice Russo

nonn

David Wells, The Penguin Dictionary of Curious and Interesting Numbers, Penguin Books, p. 103.

Harvey P. Dale, Table of n, a(n) for n = 1..3000

Cf. A049103, A049104.

SequencePosition[DivisorSigma[0,Range[1600]],{6,6}]//Flatten//Union (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Aug 23 2017 *)

More terms from Olivier Gérard

cp's OEIS Frontend

A049103 Numbers k such that k and k+1 both have 6 divisors.

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A066308 a(n) = (sum of digits of n) * (product of digits of n).

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A038400 List of pairs of consecutive numbers each with 6 divisors (duplicates removed).

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Mathematica

Extensions