cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-3 of 3 results.

A090553 Sigma(A090552(n)).

Original entry on oeis.org

1, 3, 6, 12, 12, 24, 24, 24, 72, 72, 72, 72, 144, 144, 144, 144, 144, 288, 288, 288, 576, 576, 576, 576, 576, 576, 576, 576, 1152, 1152, 1152, 1152, 1152, 1152, 1152, 2304, 2304, 2304, 2304, 2304, 2304, 2304, 2304, 2304, 2304, 2304, 2304, 2304, 4608, 4608
Offset: 1

Views

Author

Amarnath Murthy, Dec 09 2003

Keywords

Crossrefs

Cf. A007368, A090552.

Programs

  • PARI
    lista(nn) = {a = 1; print1(a, ", "); for (n = 1, nn, sa = sigma(a); a++; while (sigma(a) % sa, a++); print1(sigma(a), ", "););} \\ Michel Marcus, Oct 12 2013

Formula

a(n) = A000203(A090552(n)). - Michel Marcus, Oct 12 2013

Extensions

Corrected and extended by David Wasserman, Jan 04 2006

A237352 a(1)=1; for n>1, a(n) is the smallest positive integer for which sigma(a(n)) is a proper multiple of sigma(a(n-1)).

Original entry on oeis.org

1, 2, 5, 6, 14, 30, 66, 138, 210, 462, 930, 1974, 3810, 6510, 14322, 26670, 58674, 118110, 245730, 498666, 826770, 1720110, 3784242, 7617630, 15728610, 27524910, 53323410, 110100270, 218453970, 480598734, 853272210, 1877198862, 3413108370, 6772073070
Offset: 1

Views

Author

Michel Marcus, Apr 22 2014

Keywords

Comments

Subsequence of A090552.
The first term of A090552 that is not here is 11 since sigma(11) equals sigma(a(4)), so it is not a proper multiple.

Links

Crossrefs

Cf. A090552.

Programs

  • PARI
    lista(nn) = {n = 1; precs = sigma(n); print1(n, ", "); for (n=2, nn, if ((((ns=sigma(n)) % precs) == 0) && (ns != precs), precs = ns; print1(n, ", ");););}

Extensions

a(33)-a(34) from Hiroaki Yamanouchi, Sep 30 2014

A084403 Primes arising in A084402. a(n) = n-th partial product of A084402 - 1.

Original entry on oeis.org

2, 5, 11, 23, 47, 191, 383, 1151, 6911, 27647, 138239, 691199, 3455999, 34559999, 138239999, 414719999, 2073599999, 16588799999, 364953599999, 4744396799999, 66421555199999, 132843110399999, 664215551999999, 3321077759999999
Offset: 1

Views

Author

Amarnath Murthy, May 31 2003

Keywords

Comments

This is a sequence similar to A090552 but here with primes: a(1) = 2; for n>=2, a(n) is the smallest prime p for which p+1 is a multiple of a(n-1) + 1. - J. M. Bergot, Oct 16 2014, revised by Wolfdieter Lang, Nov 24 2014

Examples

			3-1=2, 3*2-1=5, 3*2*2-1=11, etc. are the primes arising in A084402.

Crossrefs

Cf. A084402.

Programs

  • PARI
    lista(nn) = {v = vector(nn); for (n=1, nn, v[n] = 2; while (! isprime(p=prod(i=1, n, v[i])-1), v[n]++); print1(p, ", "););} \\ Michel Marcus, Oct 31 2014

Extensions

More terms from David Wasserman, Dec 22 2004
Showing 1-3 of 3 results.

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